Turkish Prime Minister Ahmet Davutoglu has confirmed that the Turkish military has attacked Kurdish fighters in northern Syria.
The Kurdish People's Protection Units (YPG) said Turkey shot at its forces in the town of Tal Abyad on Sunday.
The YPG has been a key ally of the US in fighting the so-called Islamic State (IS) group in Syria.
Turkey fears advances by the YPG near its Syrian border could fuel separatist sentiments amongst Kurds in Turkey.
The attacks come amid increasing tensions in Turkey ahead of elections.
"We said the [YPG-aligned Democratic Union Party] PYD will not go west of the Euphrates and that we would hit it the moment it did," Mr Davutoglu told Turkish ATV television late Monday.
He gave no further details.