Turkish Prime Minister Ahmet Davutoglu confirmed Turkey attacked Kurdish forces in Syria twice, cautioning that Ankara had laid down red lines.
In a television interview on Monday night, Davutoglu said Turkey had warned the Kurdish Peoples' Protection Unit (YPG) and its political wing, the PYD, not to move west of the Euphrates River.
"We said 'PYD will not get to the west of the Euphrates. As soon as they pass, then we will shoot them.' And we shot twice," Davutolgu told A Haber channel, stressing that Turkey was a key player in Syria. He did not say when the attacks took place.
The YPG is the main ally on the ground of the United States-led coalition pushing back the Islamic State (Daesh) group.
The Kurds and their allies, including moderate Syrian rebels, have seized vast territories from the extremists in northern Syria, with the help of US airstrikes, but their offensive has stalled as they push up against areas more inhabited by Arab residents to the south.
The YPG, in a statement, said Turkish forces attacked its position three times since Sunday, but said all the incidents were east of the Euphrates.
One incident was on the eastern edge of the river, but the other two were said to be far from the Euphrates, including one near Tel Abyad, which lies 90 kilometres to the east.
To the immediate west of the Euphrates lies a 90 kilometre stretch controlled by the Islamic State group.
Ankara has long been concerned by Kurdish expansions in Syria as the YPG has links to the armed Kurdistan Workers' Party (PKK) which operates inside Turkey and has been part of a civil war since 1984.
Turkey is considered a staunch backer of certain Syrian rebel groups in the north of Syria fighting President Bashar al-Assad, including hardline Islamic factions. Some of these groups have contested territory the YPG controls.
By Shabtai Gold
Turkish Prime Minister Ahmet Davutoglu addresses the crowd during a mass campaign rally by the ruling Justice and Development Party (AKP) at Yenikapi in Istanbul on October 25, 2015
