By Zeynep Bilginsoy, Joshua Berlinger and Tim Hume


Ankara, Turkey (CNN)--Six soldiers were killed and another was wounded Thursday in a roadside bombing that hit an armored military vehicle in the southeastern Turkish province of Diyarbakir, Turkey's semiofficial Anadolu news agency reported, citing a statement from the Turkish General Staff.

Turkey blamed the attack on the PKK -- a Kurdish separatist group that Turkey, the United States and the European Union have designated a terror organization, and which Turkey has been battling for decades. It was the second deadly blast on Turkish soil attributed by Ankara to Kurdish groups in two days.

At least 28 people were killed and 61 injured in an explosion targeting military vehicles in central Ankara Wednesday, which Turkish Prime Minister Ahmet Davutoglu said was carried out by a member of the YPG, the Kurdish fighting force in Syria.

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

Turkey responded to the Ankara blast with airstrikes in northern Iraq 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 U.S. as a key partner in the fight against ISIS.

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

Kurdish denials rejected by Erdogan
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 reported by Anadolu 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, as the attack had been coordinated by actors inside and outside the country, 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 the town of Azaz in Aleppo province as it has seized upon ongoing chaos in the area to make territorial advances.

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

Military targeted
Turkey has invited the ambassadors of the five permanent members of the U.N. Security Council and Germany to the Foreign Ministry to inform them about Ankara bombing, according to a Turkish official.

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

Erdogan said that 20 of those killed were military personnel.

Video aired on CNN Turk showed large flames reaching toward the night sky from an area on the ground. Lights from numerous emergency vehicles flashed nearby.

Allies split over support for Kurdish groups
The attacks will increase tensions between Ankara and its allies over their relationship with Kurdish forces in Syria.

The Kurds, an ethnic minority spread in the intersecting parts of Turkey, Syria, Iran and Iraq, have long wanted their own independent 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.'s campaign against the terror group.

That's drawn the ire of Erdogan, who said last week the U.S. is responsible for a "sea of blood" in Syria because of its support for the YPG.

U.S. State Department spokesman John Kirby responded by saying the U.S. 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.

Erdogan vows strong response
Turkey's PM referred to the split over how the YPG was viewed in comments following the Ankara bombing Wednesday.

"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 President 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 at the weekend prompted the U.S. 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 the attacks.

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

His thoughts were echoed by U.S. Defense Secretary Ash Carter.

"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," he said.

The Russian Foreign Ministry said in a statement 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."

CNN's Jason Hanna, Hamdi Alkhshali, Yousuf Basil, Christine Theodorou, Arwa Damon, Alla Eshchenko and Greg Botelho contributed to this report.