Near Mosul, Iraq (CNN)Iraqi-led forces engaged Thursday in the most intense fighting yet in the battle to liberate the city of Mosul from two years of brutal ISIS rule, on day four of an offensive that's been met with fierce resistance from ISIS fighters.
But with the clashes have come sweeping gains -- the coalition has now recaptured at least 100 square kilometers of territory, a CNN analysis of the battlefield shows.
Iraqi Maj. Gen. Maan al-Saadi said 200 ISIS fighters were killed as Iraqi forces took the Christian town of Bartella from ISIS militants, the latest territorial win for a coalition of around 100,000 people quickly closing in on Mosul.
The Iraqi-led coalition launched the operation on Monday to retake Mosul, seen as the cultural capital of ISIS's envisaged caliphate, or so-called Islamic State.
Latest Developments
• A US service member was killed Thursday in northern Iraq, the US military aid. The Pentagon didn't say whether the service member was taking part in the Mosul offensive.
• Saadi acknowledged pockets of resistance in Bartella, saying they would be cleared before nightfall Thursday.
• Nine suicide trucks laden with explosives were destroyed before they reached Iraqi positions, he said.
• Dozens of Yazidi women enslaved by ISIS in Iraq have been transferred to Raqqa in Syria, a UK-based monitor says.
• Iraqi military officials say armored military vehicles are now stationed some 4 miles from the city.
An Iraqi special forces soldier looks for danger as he drives to the front lines of Bartella.
The operation is going faster than expected, Iraqi Prime Minister Haider al-Abadi said earlier Thursday, as Peshmerga fighters opened a new front from the north, liberating several villages from ISIS control some 20 kilometers from Mosul.
A CNN team in various locations near Mosul said Thursday was the most intense so far in terms of the number of clashes that were taking place and the variety of forces engaged.
The 100,000-strong coalition brings together Iraqi security forces, Kurdish Peshmerga fighters and several paramilitary groups representing religious minorities, including Shia and Christian Iraqis.
It marks an extraordinary union between factions that have long stood on opposing sides in Iraq's history.
Concerns for civilians
Forces have faced fierce resistance in some pockets, coming under heavy gunfire and suicide bomb attacks, but overall the operation has made sweeping gains.
Iraqi soldiers in Qayyarah, 35 miles south of Mosul, as forces push toward the key city
"The fighting forces are currently pushing forward toward the town more quickly than we thought and more quickly, certainly, than we had established in our planned campaign," Abadi said, according to a translation, via teleconference to a ministerial-level meeting on Mosul in Paris.
"Our road forward is a long one, and we need to continue to work to destroy terrorism and put an end to this kind of destruction."
As reports emerge of people remaining trapped in Mosul and others being dragged into abandoned towns as human shields, there is growing concern of a bloody toll on civilians as coalition forces bombard targets in support of ground forces.
An Iraqi man escapes the thick black smoke of an oil field set on fire in Qayyarah
Abadi said he had instructed "the military on all the fronts to open corridors to citizens and IDPs (internally displaced people), to all the people who want to flee the fighting."
Peshmerga offensive on three fronts
The Peshmerga said its offensive, on three fronts, would capitalize on gains made by Kurdish and Iraqi forces in recent days, according to a news release on Thursday from the the Peshmerga's General Command.
Bullet cases at the front line east of Bartella 18 kilometers from Mosul. Iraqi counterterror forces battled ISIS militants on the outskirts of the city.
"The objectives are to clear a number of nearby villages and secure control of strategic areas to further restrict ISIL's movements," the statement said, using an alternative name for ISIS.
The new offensive centers on an ISIS-held Christian village, Batnaya, about 20 kilometers north of Mosul, captured by ISIS in 2014.
Iraqi forces and a Christian paramilitary group surrounded another Christian town -- Hamdaniya, also known as Qaraqosh -- on Wednesday and are still battling ISIS fighters there, who have put up a fierce resistance. Militant targets there were also bombarded by coalition forces Wednesday.
Exploring ISIS tunnels near Mosul 02:24
The coalition's members vastly outnumber their opponents. Up to 5,000 ISIS fighters are in Mosul, a US military official said. The terror group's supporters put the number at 7,000.
Peshmerga forces have discovered several ISIS tunnels -- part of the group's elaborate defenses. In some, dishes of food were still warm, showing how close forces are coming to fighters before they flee.
ISIS tightens noose on Mosul residents
Meanwhile, a US general claimed that some local ISIS leaders are fleeing the city.
"We are telling Daesh that their leaders are abandoning them, and we have seen movement out of Mosul," US Army Maj. Gen. Gary Volesky said in a video briefing from Baghdad, referring to ISIS by its Arabic acronym.
Why Mosul matters
Since Mosul's capture by ISIS fighters in June 2014, Mosul has been a vital stronghold for ISIS.
The largest city under ISIS control in Iraq and Syria, it was the city from which the group first declared the establishment of its so-called caliphate.
Since then, ISIS has gradually lost its other Iraqi cities -- Ramadi, Tikrit and Falluja -- to government forces. About 1 million people are estimated to remain in Mosul, once a cosmopolitan trade hub of 2 million residents.
ISIS distributed leaflets Wednesday evening to residents, demanding they hand over their mobile phone SIM cards and remove all antennas from the roofs of their homes. ISIS representatives will collect the SIM cards over the next 24 hours, according to the leaflets. Anyone who fails to comply will be arrested, the leaflets claim.
ISIS has release a slew of propaganda videos over the years from cities under its control, and often showed Mosul as a bastion of peace and order under its rule. But residents who have fled the city say they lived a life of fear.
Photos: Mosul: Iraqi-led forces push into key city
Members of the Iraqi federal police wave the country's flag as they celebrate in the Old City of Mosul on July 9, 2017. Iraq declared victory against ISIS forces in Mosul after a grueling monthslong campaign. The battle to reclaim Mosul, the last major ISIS stronghold in Iraq, has been underway since fall 2016.
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This injured girl was found by Iraqi forces as they advanced against ISIS militants in the Old City of Mosul on Monday, July 3. She was carried away for medical assistance.
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A suspected ISIS fighter is held in a basement while Iraqi forces continue to push for control of the Old City of Mosul on Monday, July 3.
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An Iraqi Special Forces soldier exchanges fire with ISIS militants in the Old City on Friday, June 30.
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A bomb explodes near the al-Nuri mosque complex on Thursday, June 29. Iraq's military has seized the remains of the Great Mosque of al-Nuri. Iraq and the United States have accused ISIS of blowing up the historic mosque.
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Members of the Iraqi Federal Police hold a position as US-led coalition forces advance through the Old City on Wednesday, June 28.
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The remnants of Mosul's ancient leaning minaret are seen in the Old City on Sunday, June 25. ISIS' claim that US warplanes were responsible for the destruction of the minaret is "1,000% false," US officials told CNN.
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Two boys comfort each other after their home collapsed during fighting between Iraqi forces and militants in Mosul on Saturday, June 24. The boys, who are cousins, said some of their relatives were still under the rubble.
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An Iraqi soldier helps transport a girl as residents flee their homes west of Mosul on Friday, May 26.
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Displaced Iraqis make their way through rubble after evacuating their homes in a neighborhood of west Mosul on Wednesday, May 17.
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An Iraqi man tries to extinguish a burning car during fighting in Mosul's western Rifai neighborhood on Tuesday, May 16.
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A member of the Iraqi counterterrorism service secures a building as troops push toward Mosul's Al-Oraibi western district on Sunday, May 14.
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A smoke cloud rises on the front line as the Iraqi Emergency Response Division advances in west Mosul on Saturday, May 6.
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A wounded man is transported in western Mosul on Friday, April 21.
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An Iraqi federal policeman smokes during a break from battle on Wednesday, April 12.
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A member of Iraq's security forces stands guard in eastern Mosul as smoke rises from the ISIS-controlled western section of the city on Friday, April 7.
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Iraqis visit a bath house on the southern outskirts of Mosul on Wednesday, April 5.
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Flames billow from an explosion in Mosul during a clash between Iraqi forces and ISIS fighters on Sunday, March 5.
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Families are forced to evacuate as Iraqi forces advance in western Mosul on Thursday, March 2. The number of internally displaced people has surged as the offensive effort has intensified.
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Mosul residents cross a damaged bridge in the al-Sukkar neighborhood on Saturday, January 21.
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French President Francois Hollande and French Defense Minister Jean-Yves Le Drian, right, view territory held by ISIS during a visit to a military outpost near Mosul on Monday, January 2.
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A young girl takes part in a Christmas Day Mass at a church in the predominantly Christian town of Qaraqosh. The area's churches were heavily damaged by ISIS militants before the town was freed by Iraqi forces during the Mosul offensive.
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Iraqi Shiite fighters ride through a desert area near the village of Al-Boutha al-Sharqiyah, west of Mosul, on Friday, December 2.
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Internally displaced Iraqis who fled the fighting in Mosul watch as a civilian drone films them at the al-Khazir camp on Thursday, December 1.
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An Iraqi soldier searches a home for ISIS militants after Iraqi forces retook the village of Al-Qasr on Wednesday, November 30.
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Iraqi soldiers transport a comrade who was injured during a battle near the village of Haj Ali on Tuesday, November 29.
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A man mourns during the funeral of four Iraqi paramilitary fighters who were killed in battles in the town of Tal Afar.
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Displaced civilians return to the village of Tall Abtah on Friday, November 25, after Iraqi forces retook the village from ISIS.
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Iraqi civilians sit on the ground in Mosul on November 24. An Iraqi officer addressed the group, demanding to know the whereabouts of alleged ISIS militants who opened fire on troops a few days earlier.
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An injured baby receives treatment at a field hospital in Mosul on November 15.
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A woman cries Sunday, November 13, after seeing the St. Addai church that was damaged by ISIS fighters during their occupation of the Keramlis village.
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An Iraqi special forces soldier prays next to a Humvee before troops pushed toward Mosul's Karkukli neighborhood on November 13.
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A Kurdish Peshmerga fighter holds part of a defused bomb planted by ISIS militants in Bashiqa, Iraq, on Friday, November 11.
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A member of Iraq's special forces guards two suspected ISIS fighters found hiding in a house in Mosul on November 11.
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An Iraqi woman displaced by war holds her cat near a checkpoint in the Iraqi village of Shaqouli, east of Mosul, on November 10.
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Iraqi troops watch a broadcast of Donald Trump's acceptance speech in a house in Arbid, on the outskirts of Mosul, on Wednesday, November 9. Iraqi Prime Minister Haider al-Abadi congratulated Trump on his win and said he hoped for continued support in the war on ISIS.
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US Marines install equipment at a coalition base in Qayyara on November 9.
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An Iraqi forces member investigates a mass grave that was discovered after coalition forces recaptured the area of Hamam al-Alil on Monday, November 7.
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Iraqi children witness a man being interrogated by a member of the Iraqi army at a base next to the Al-Intissar neighborhood of Mosul on November 7.
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A civilian man who fled the fighting trims his beard after reaching an Iraqi army position in Mosul on November 7.
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Children play in debris created by an airstrike in Qayyara on Sunday, November 6.
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Female members of the Freedom Party of Kurdistan sing as they hold a position near Bashiqa on November 6.
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A baby is passed through a fence back to his mother at a refugee camp in the Khazir region on Saturday, November 5.
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People line up to receive food at a refugee camp in the Khazir region on November 5. Thousands are taking refuge in camps set up for internally displaced people.
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Iraqi soldiers pass near a bridge destroyed in an airstrike in Qayyara on November 5.
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Iraqi soldiers patrol an alley on the outskirts of Mosul on Friday, November 4.
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A suspected member of ISIS is detained at a checkpoint near Bartella, Iraq, on November 4.
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Iraqi families pack into a truck to be moved to camps on Thursday, November 3.
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An Iraqi special forces soldier searches for the location of an ISIS sniper in Gogjali on November 1.
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A man fleeing the village of Bazwaya carries a white flag as he arrives at a checkpoint on November 1.
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An Iraqi soldier receives treatment after being injured during clashes with ISIS fighters near Bazwaya on October 31.
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An Iraqi soldier navigates through a shattered windshield as coalition forces advance on Bazwaya on October 31.
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Archbishop Yohanna Petros Mouche, center, performs Mass in the liberated town of Qaraqosh on Sunday, October 30.
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Children play in a camp for internally displaced people near Kirkuk, Iraq, on October 30. More than 600 families from Tel Afar, a town west of Mosul, have been living in the camp since ISIS took control of the area in 2014.
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Displaced families are seen on the road near Qayyara on Saturday, October 29.
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U.S. military personnel take cover in a bunker after a mortar alarm was sounded at a coalition air base in Qayyara on Friday, October 28.
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Women and children grieve over the grave of a family member at a Qayyara cemetery damaged by ISIS on October 27.
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Residents of Qayyara wait for distribution of food and water rations on October 26. Local water sources have been contaminated by the burning oil and sulfur.
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Iraq's counterterrorism forces advance toward ISIS positions in Tob Zawa on October 25.
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Soldiers give first aid to an injured boy in Tob Zawa on October 25.
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Kurdish Peshmerga forces take positions as they start to move toward the Imam Reza and Tizxirab villages of the Bashiqa district on Sunday, October 23.
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Iraqi forces distribute fruit in the village of al-Khuwayn, south of Mosul, after recapturing it from ISIS on October 23.
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Kurdish security forces detain a suspected member of ISIS in the eastern suburbs of Kirkuk on Saturday, October 22.
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An Iraqi forces member helps a man push a car as they arrive at a refugee camp in Qayyara on October 22.
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Spent bullet cartridges litter the street around the Jihad Hotel, where ISIS militants battled Iraqi security forces in Kirkuk on Friday, October 21.
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Gen. Abdel Ghani al-Asadi, who leads Iraq's counterterrorism forces, sits in Bartella on October 21 after the town was reclaimed.
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Peshmerga fighters look over a village during an assault near Bashiqa on Thursday, October 20.
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Iraqi forces head toward the front lines near Qayyara on Tuesday, October 18.
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A Peshmerga fighter peers up from an underground tunnel in the liberated town of Badana on October 18. ISIS fighters have built tunnels below residential streets to escape from airstrikes.
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Kurdish security forces take up a position near ISIS-controlled villages on Monday, October 17.
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Smoke rises from a suicide car bomb attack carried out by ISIS in the village of Bedene on October 17.
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Members of the Iraqi coalition gather around a fire at Zardak mountain ahead of the offensive.
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Peshmerga forces deploy in the dark near the village of Wardak early on October 17.
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Those who have managed to flee are now telling their stories, offering a glimpse into life under ISIS's harsh rule.
Iraqi refugees debunk ISIS' portrayal of Mosul 02:12
Iraqis who were once swayed by the slick productions that ISIS posted on social media soon learned of the privations and violence that permeated the cities that the group occupied.
A unit of what appeared to be US special forces advisers entered ISIS territory with the very first armored convoy of Peshmerga on Monday, a CNN team observed. It followed a dozens-strong unit of Kurdish armor that was bound towards ISIS positions, placing American forces right at the front of the opening moments of the fight to retake Mosul.
