Turkey has sent armour and missile batteries to areas bordering Kurdish parts of northern Syria, where opposition groups say President Bashar al-Assad's forces have ceded territory to a group allied to the PKK.
There has been no indication Turkish troops would cross the border, but NATO-member Turkey has warned any attack emanating from a PKK presence in northern Syria could give it reason to intervene. Ankara has repeatedly bombed and sent troops into parts of Kurdish-run northern Iraq where the PKK has camps.
Tanks and missile batteries conducted manoeuvres one km (less than a mile) from the Syrian border in the Suruc district of Şanlıurfa province, directly across from one of the Syrian towns reportedly controlled by Syria's Democratic Union Party (PYD), the political offshoot of the PKK in Syria.
Ankara, which has tried and failed to crush the PKK's 27-year-old campaign for autonomy in largely Kurdish southeastern Turkey, is alarmed by the prospect that a power vacuum in Syria could embolden its own Kurdish separatists.
Turkey's foreign minister raised the issue of the Syrian government's loss of control over territory with the president of the autonomous Kurdish region of northern Iraq on Wednesday.
"Any attempt to exploit the power vacuum by any violent group or organisation will be considered as a common threat, which should be jointly addressed," the foreign ministry said following Foreign Minister Ahmet Davutoğlu's talks with Massoud Barzani, head of Iraq's Kurdistan region.