Turkey has blamed a devastating bomb blast targeting a military convoy in Ankara on Kurdish rebels, and has vowed to respond sharply, raising concerns of an escalation in ongoing violence both at home and in Syria.
28 soldiers were killed and scores more were injured in the attack, which occurred early Wednesday evening.
Notably, on Thursday Turkish Prime Minister Ahmet Davutoglu accused not just the Kurdistan Workers Party (PKK) - a Kurdish militant group locked in a decades-long battle for greater rights with Turkey - but also its Syrian Kurdish sister faction, the Syrian Kurdish Democratic Union Party (PYD).
Those claims in particular - which have not yet been confirmed - will raise fears that Turkey could use the attack as a pretext to launch a limited ground operation inside Syria, something it has been suggesting for several months to stem Kurdish advances.
"It has been revealed that this attack was carried out by members of the terrorist organisation in cooperation with a YPG member who infiltrated (Turkey) from Syria," Davutoglu told reporters in Ankara, referring to the PYD's armed wing, the People's Protection Units.
Davutoglu claimed that the bomber was a Syrian national named Salih Necar, and said nine people had already been detained over the attack.
But PYD leader Salih Muslim denied his fighters played any role in the bombing, and suggested the accusations by Turkey were motivated by Ankara's need to find a pretext to launch a ground operation against Kurdish forces in Syria.
"We deny any involvement in this attack," Muslim told the AFP news agency on Thursday morning.
"These accusations are clearly related to Turkish attempts to intervene in Syria," he added.
Turkish warplanes overnight struck PKK positions in northern Iraq in retaliation for the attack, but Turkey is unlikely to end its response there.
President Recep Tayyip Erdogan has already threatened a harsh response.
"Our determination to respond in kind to attacks taking place inside and outside our borders is getting stronger with such acts," he said shortly after the attack. "It must be known that Turkey will not shy away from using its right to self-defense at any time, any place or any occasion."
The timing of the attack is notable, in that it follows five days of artillery bombardment by Turkish forces of YPG-held territory along the Syrian border, provoking warnings of retaliation by the YPG. It also comes at a time when both Turkey and Saudi Arabia have repeatedly raised the prospect of launching a ground operation inside Syria to bolster rebel forces, who are reeling in the face of regime advances backed by devastating Russian air power, as well as recent lightening advances by the Kurds in the north.
Ankara has been alarmed at the rapid advances made by Kurdish forces and their local Arab allies against both ISIS in the northeast, and against Turkish-backed Islamist rebels - including Al Qaeda's Nusra Front - in northwestern Syria. The PYD has declared it wishes to unite all Kurdish-ruled areas or "cantons" in northern Syria to create a contiguous autonomous Kurdish region - an objective the Turkish government has vowed to block.
On Wednesday, Turkey confirmed it had facilitated the transport of some 500 Islamist rebels to Azaz in northern Syria, where beleaguered rebels are attempting to fend-off a Kurdish advance.
But Kurdish forces have continued to take advantage of a major regime operation against the rebels - thanks to Russia's relentless air campaign and increased support for the regime from Iran and Hezbollah - to launch their own advances against already beleaguered rebel forces.
As Turkey's indirect efforts to stem rebel losses come to naught, could this be the pretext Ankara was looking for to launch its own ground incursion into Syria?