Turkey's military on Sunday fired artillery shells at a Kurdish militia in Syria that is backed by the United States but deemed a terrorist group by Ankara, the state-run Anadolu news agency reported.
The shelling targeted YPG positions on the eastern bank of the Euphrates River in northern Syria, Anadolu said.
Turkish President Recep Tayyip Erdogan has repeatedly threatened to launch a new offensive in Syria east of the Euphrates, and on Friday said he was giving the YPG a "final warning".
Anadolu reported that the strikes, which hit a hill near the Zur Maghar village across the Euphrates from the city of Jarablus in the Aleppo province, were in response to fire from the area.
The shelling comes a day after Erdogan hosted a summit in Istanbul on the Syrian conflict with the leaders of Russia, France and Germany.
The YPG, which holds swathes of northern and northeastern Syria, forms the backbone of the Syrian Democratic Forces (SDF), the Kurdish-Arab alliance that has received extensive American support in the fight against the Islamic State (IS) militant group in the war-torn country.
However Ankara is bitterly opposed to the YPG, regarding it as an extension of the Kurdistan Workers' Party (PKK), which has waged a deadly insurgency in Turkey since 1984. The PKK is designated as a terror group by Turkey and its Western allies.
Washington's support of the YPG remains a major point of contention between the US and Turkey, and a large-scale offensive east of the Euphrates could aggravate already tense relations between the NATO allies.
Turkey has also repeatedly threatened an attack on the YPG-controlled Syrian city of Manbij, where US troops are deployed.
To ease tensions, Washington and Ankara agreed to have troops conduct coordinated patrols around the city, and such a patrol went ahead on Sunday, Turkish armed forces said.
Earlier this year, Turkey launched operation "Olive Branch" in Syria west of the Euphrates, successfully ousting YPG forces from their enclave in Afrin.
Ankara has long opposed the YPG controlling a continuous stretch of territory on its border up to Iraq, fearing the creation of an autonomous region or even independent entity that could embolden Turkey's own Kurds.