The Turkish government Thursday blamed Syria's main Kurdish militia as well as Kurdish separatists in Turkey for the bombing in Ankara that killed 28 people, and vowed retaliation.
"The assailants have all been identified," Turkish Prime Minister Ahmet Davutoglu said about Wednesday night's attack in the Turkish capital, pointing to a Syrian national born in 1992.
The fighter from the People's Protection Units (YPG) - the Kurdish militia in Syria - carried out the attack "with the support of a terrorist organization," Davutoglu said, referring to the banned Kurdistan Workers' Party (PKK) in Turkey.
No group has yet claimed responsibility for the car bombing, which targeted the military in a key government district of Ankara and also injured 61 people.
It took place near an air force headquarters and in the vicinity of the parliament. Davutoglu said 27 soldiers and one government official were killed.
Syrian Kurdish leader Salih Muslim told dpa that Turkey's accusations against the YPG are an attempt at escalation.
"We totally reject these accusations. We have no link with what is happening inside Turkey," Muslim, leader of the Democratic Union Party (PYD), which is close to the YPG, said by telephone.
"These accusations are part of the Turkish escalatory policies against the Kurdish parties," Muslim charged.
The YPG has the backing of both Russian and US airstrikes as it advances against the Islamic State extremist group in Syria. Turkey's government is increasingly concerned about the YPG's gains there since it has ties to the PKK, which has been in conflict with the Turkish state for more than 30 years.
The Turkish premier vowed retaliation and warned that "all necessary measures will be taken against [YPG and PKK] anywhere and under any circumstances."
He condemned the YPG for being a "a pawn of the Syrian regime and the regime is directly responsible for the Ankara attack. Turkey reserves the right to take any measure against the Syrian regime."
PKK commander Cemil Bayik told the Firat news agency, which is affiliated to the Turkish group: "We do not know who did it. But it could have been in retaliation for the massacres in Kurdistan."
President Recep Tayyip Erdogan stressed that even if PKK and PYD leaders claim they had nothing to do with the Ankara attack, evidence and documents from the intelligence services and Interior Ministry point to their involvement.
He said 14 suspects were arrested and that the number will likely rise.
The Turkish military has for weeks been battling the PKK in the mostly Kurdish south-east of the country.
At least six Turkish soldiers were killed Thursday and one was wounded after a bomb attack in the south-eastern province of Diyarbakir, the military said, and blamed it on the PKK.
In October, a twin suicide bombing in Ankara killed 100 people and was blamed on the Islamic State extremist group. Authorities also blamed Islamic State, which operates in neighbouring Iraq and Syria, for a bombing in Istanbul last month that killed 11 German tourists.
German Chancellor Angela Merkel expressed her condolences and assured Davutoglu on Wednesday that her country would support Turkey in the fight against terrorism. She also spoke with Erdogan on Thursday.
Merkel later joined other EU leaders in pledging to step up their fight against the "scourge" of terrorism.
"Acts of terrorism, by whomever and wherever they take place, are always unacceptable," the leaders said in a joint statement issued during an EU summit in Brussels, condemning the attack.
Russia also condemned the Ankara attack as a "barbaric crime" that "cannot be justified," and said its "organizers must be held accountable."
The traditionally warm relations between Moscow and Ankara soured after Turkey shot down a Russian warplane in November for allegedly violating Turkish airspace - a charge Russia denies.
But on Thursday, the Russian Foreign Ministry said in a statement that the bombing in Ankara "once again shows the necessity of uniting all states in the fight against international terrorism."
Russia and Turkey support opposing sides in the Syrian civil war. Russia backs Syrian President Bashar al-Assad, whereas Turkey, a NATO member, supports rebels trying to overthrow al-Assad.