Turkish Prime Minister Recep Tayyip Erdogan has accused Syria of giving Kurdish rebels a free hand in its north and warned that Ankara would not hesitate to strike.
"In the north, it (President Bashar al-Assad's regime) has allotted five provinces to the Kurds, to the terrorist organisation," Erdogan said on Turkish television Wednesday, referring to the Kurdistan Worker's Party (PKK).
He said the move was explicitly directed against Turkey and warned that "there will undoubtedly be a response on our part to this attitude", adding that rebels had put up posters of jailed leader Abdullah Ocalan in the area.
Ocalan, one of the founders of the PKK, was jailed for life in 1999.
Asked if Ankara would strike fleeing rebels after an attack on Turkish soil, Erdogan said: "That's not even a matter of discussion, it is a given. That is the objective, that is what must be done."
"That is what we have been doing and will continue to do in Iraq," he said.
"If we occasionally launch air strikes against terrorist areas it's because of defence needs."
Turkey regularly bombs suspected Kurdish rebel hideouts in northern Iraq.
The PKK, listed as a terrorist organisation by Turkey and by much of the international community, took up arms in Kurdish-majority southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives.
Relations between Turkey and Syria have steadily soured since the start of the uprising against Assad's rule in Syria in March 2011, with Erdogan vehemently criticising the regime's brutal crackdown.
In northern Iraq, Kurds have carved out a semi-autonomous region since the US invasion of 2003, and fears are on the rise in Turkey that the same could happen on their doorstep in northern Syria.
Erdogan told a news conference Thursday that creating a buffer zone on the border was one of the options.
"This could one of the alternatives. A security zone, a buffer zone all these could be part of the alternatives," he said, without explaining how this would be implemented.
He said Foreign Minister Ahmet Davutoglu would visit Arbil in northern Iraq next Wednesday to share Ankara's "sensitivity and determination" on the issue with the autonomous Kurdish administration.
Turkey has send batteries of missiles and extra troops to the border with Syria and has also closed three frontier posts to Turkish nationals after rebels fighting Assad wrested control of corresponding posts in Syria.
Turkish newspapers have published alarmist reports with pictures of Kurdish flags fluttering from buildings in northern Syria and said parts of the region had fallen into the hands of the PKK or its Syrian branch, the Democratic Union Party (PYD).
"It is not hard to predict that the PKK will strengthen its presence in this climate," wrote columnist Fikret Bila in the Milliyet newspaper.
If they do manage to take control of the region, "it will be possible for the (PKK) to launch attacks into Turkey from the Syrian border," he added.
The head of the opposition Syrian National Council said this week that Syrian forces had "entrusted" the northern region to the PKK or the PYD and then withdrawn.
The Kurdish question has long played a role in tricky relations between Turkey and Syria, where Kurds make up less than 10 percent of the population and have long complained of discrimination and repression.
The neighbours came to the brink of a war in the 1990s over Syria harbouring Ocalan at the time.
Relations warmed after Erdogan's moderate Islamist Justice and Development Party took power in Turkey in 2003 but ties have plummeted again over the Syria conflict.