(CNN)Syrian regime forces have broken a three-year ISIS siege of the eastern city of Deir Ezzor, Syria's official news agency SANA reported.
Quoting a reporter on the ground, SANA said "advancing forces coming from the western front met guards of Regiment 137 on Tuesday afternoon, and thus, broke the siege imposed by ISIS terrorists on the city."
Regiment 137 refers to a group of Syrian regime soldiers who have been trapped in Deir Ezzor for nearly three years.
With ISIS under increasing pressure in Raqqa -- its self-declared caliphate -- the strategic Deir Ezzor had been viewed as the terror group's last major position in Syria.
"Here you are today side by side with your peers who gave everything for your victory and waged the hardest of battles to break the ring around the city," SANA quoted President Bashar al-Assad as telling Syrian soldiers.
"So that your peers can be with you on the first lines of attack to cleanse the entire area of the filth of terrorism and to restore safety and security across the country until the very last inch."
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The Syrian news agency said army units had earlier carried out "new military operations under an intensive air cover to break the siege imposed by the ISIS terrorists on Deir Ezzor city."
An unspecified number of ISIS fighters were killed and at least 10 vehicles in an ISIS convoy were destroyed in Syrian air strikes.
Russia said it backed the Syrian army's offensive with cruise missiles fired from the Admiral Essen frigate of the Black Sea Fleet. Its defense ministry claimed the elimination of ISIS in the area would mark a "strategic defeat" for the extremist group.
"The missiles were launched at targets in accordance with data received through intelligence channels," the Russian defense ministry said on its Facebook page.
It said the missile strikes were conducted on a fortified area located in the suburbs of a town called Ash Sholah under the control of ISIS fighters, most of them from Russia and former countries of the Soviet Union.
As well as backing the advance of the Syrian army on Deir Ezzor, the Russian missile assault also meant an end to ISIS' plans to regroup in Ash Sholah, the Russian defense ministry said.
An ISIS ammunition depot was also wiped out in al-Bghiliyeh village in the western countryside of the province, SANA said. As the army advanced, it destroyed many other ISIS vehicles, including cars rigged with explosives.
In neighboring Iraq, government forces have recently driven ISIS Fighters from Mosul and Tal Afar.
