Kurdish-led forces who recently captured the northern Syrian city of Minbij from Islamic State jihadists said Monday they had come under artillery shelling from the Turkish military.
Turkish artillery shelled defensive positions of the Minbij Military Council 20 kilometres from the border, in an area where they had recently clashed with Islamic State militants, council spokesman Shervan Darwish told dpa.
The alleged shelling came after Turkish Foreign Minister Mehmet Cavusoglu said the border area must be "cleansed" of Islamic State.
The Kurdish-led Democratic Forces of Syria (DFS), which includes the Minbij Military Council, have expelled Islamic State from much of northern Syria with the backing of US-led airstrikes.
They say they have now established defensive lines along the Sajur river, south of Jarabulus, the last major town on the border held by Islamic State.
Syrian rebel factions are meanwhile planning to launch an attack on Jarabulus from Turkish soil with the backing of Ankara, two fighters told dpa on Monday, speaking on condition of anonymity.
At the weekend, Turkish Prime Minister Binali Yildirim said Ankara would be "more active" in Syria in the coming six months, without specifying plans.
The two rebel fighters, one from the Islamic Jabhat al-Shamiya and one from the Hamza Brigades, said the US does not support the latest operation, planned by Turkey.
In the past, Turkey, which lets some rebel factions operate in the south of the country, has moved fighters from one part of northern Syria to another to launch attacks, crossing through Turkish soil.
The offensive risks upping long-standing tensions between the rebels and the Kurdish-led DFS. The Jarablus Military Council, a group seen as close to the DFS, called on the United States to prevent a Turkish-led intervention.
The developments come two days ahead of an expected visit to Ankara by US Vice President Joe Biden.
The US has been wary of some hardline factions which Turkey supports, though it has backed some Islamist groups during the course of the five-year civil war.
Turkey, for its part, has complained repeatedly about the Kurdish fighters advancing against Islamic State, insisting it would not tolerate the Kurdish YPG militia - the main element of the DFS - gaining ground inside Syria along the border.
Ankara is concerned by the YPG's link to Kurdish fighters inside Turkey but says it has received assurances from the US that YPG forces would withdraw from Minbij after it had been captured, leaving the town in the hands of local fighters.
On Saturday night, a suicide bomber killed 54 people at a Kurdish wedding in Gaziantep, southern Turkey. Authorities have blamed Islamic State.