Turkish soldiers die in attack a day after Ankara explosion

"It has been revealed that a YPG member who infiltrated from Syria with members of the separatist terror organization conducted this attack," Turkish Prime Minister Ahmet Davutoglu said, identifying the YPG member as Syrian-born Saleh Najar.

Turkey responded to the Ankara blast with airstrikes in northern Iraq on Wednesday night targeting the PKK, which it says is affiliated with YPG.

The YPG is the 30,000-strong armed wing of the PYD, the main Kurdish political actor in Syria, and receives backing from the United States as a key partner in the fight against ISIS. Turkey considers it a terror group and indistinguishable from the PKK.

The Turkish General Staff said that 60 to 70 people, including some of the PKK's top figures, were targeted Wednesday night in northern Iraq's Haftanin region close to Turkish border, according to Anadolu. Northern Iraq is home to the majority of that country's Kurdish population.

The Kurds, an ethnic minority spread in the intersecting parts of Turkey, Syria, Iran and Iraq, have long sought an independent state.

There has been no reported claim of responsibility for the Ankara bombing, and the PYD, YPG and PKK have all denied involvement.

A top PKK leader, Cemil Bayik, said his organization did not know who carried out the bombing.

"We know there are people who have conducted such acts before as retaliation of massacres in Kurdistan," Bayik said in an interview with the PKK-affiliated Firat News Agency. "Those who conducted the attack will probably announce why soon."

But in comments that Anadolu reported Thursday, Turkish President Recep Tayyip Erdogan rejected the denials, saying evidence provided by Turkey's Interior Ministry pointed to the Kurdish groups.

Fourteen people had been arrested in connection with the Ankara bombing, he said, adding the number was likely to rise, according to Anadolu.

"The Ankara bomb indicates that Turkey's (military) operation yields serious results in face of recent terror," he said, according to the agency.

Turkey has been shelling YPG positions in northern Syria recently, targeting the group around Azaz in Aleppo province amid an uptick in Kurdish military gains in the region.

Ankara has said the bombardment was a response to shelling from YPG positions.

Wednesday's explosion hit three military vehicles and a private vehicle in central Ankara near the Turkish Parliament buildings, Anadolu reported, citing Ankara Gov. Mehmet Kiliclar. The vehicles were stopped at a traffic light, the military said.

Authorities suspect a bomb-laden vehicle caused the explosion, Kiliclar said, according to Anadolu.

Erdogan said that 20 of those killed were military personnel.

Turkey invited ambassadors from the five permanent members of the U.N. Security Council, Germany, the Netherlands and an European Union delegation to the Foreign Ministry to inform them about the bombing, according to a Turkish official.

The attacks will increase tensions between Turkey and its allies over their relationship with Kurdish forces in Syria as Ankara wages parallel campaigns against ISIS and PKK rebels.

Turkey is alarmed that the YPG now controls much of the Syrian border with Turkey and is essentially creating a state within a state.

While Turkey views the YPG as a terrorist group, and its associated political party, the PYD, as an affiliate of the PKK, Ankara's American allies hold a different view.

The YPG has been one of the most successful forces in taking the fight to ISIS, and has proved a vital partner in the U.S. campaign against the Islamist terror group.

That's drawn the ire of Erdogan, who said last week the United States is responsible for a "sea of blood" in Syria because of its support for the YPG. The links between the YPG and PKK were apparent during a CNN trip to a Kurdish-held area of northern Syria in October -- portraits of Abdullah Ocalan, the PKK's imprisoned leader, hung from walls, while some YPG fighters admitted they had come from Turkey to join the battle.

U.S. State Department spokesman John Kirby responded to Erdogan's criticism by saying Washington understood Ankara's viewpoint but begged to differ.

"We recognize that the Turks do (label the PYD as terrorists), and I understand that. Even the best of friends aren't going to agree on everything," Kirby said.

Turkey's Prime Minister referred to the split in views of the YPG in comments following Wednesday's Ankara bombing.

"YPG is part of the separatist terror organization," Davutoglu said, referring to the PKK. "This was already known to us, but we hope this act shows all our allies and the world this fact."

And, days ahead of a "cessation of hostilities" in Syria set to take effect Friday, Erdogan warned of a strong Turkish response, raising the specter of an escalation of strikes against the YPG across the Syrian border.

Concerns over Turkey's shelling of the YPG over the weekend prompted the United States and France to urge restraint, and Syria to call on the U.N. Security Council it to intervene.

"Our determination to respond in kind against such attacks against our unity and future from outside and inside is even more strengthened through such attacks," Erdogan said in a statement after Wednesday's attacks.

"Turkey will not hesitate to use its right to self-defense anytime, anywhere, and in all situations."

U.S. Defense Secretary Ash Carter echoed Erdogan's remarks.

"We strongly condemn this cowardly attack which appears to have targeted buses carrying Turkish military personnel. We stand with our Turkish allies in the face of this horrific act, which only strengthens our resolve to deepen our ongoing cooperation in the fight against terrorism," Carter said.

The prospect of increased Turkish actions against Syrian Kurdish forces also threatens to raise tensions further between Ankara and Moscow, which has provided air cover to the YPG.

In a statement reacting to this week's Ankara bombing, the Russian Foreign Ministry said that "there's no justification for barbaric crime. Its organizers and masterminds have to pay for what they've done. What happened, once again, shows the need of a unity of all states in fight against international terrorism."