The United States on Friday warned Turkey not to disrupt operations by US and Kurdish forces against jihadists in Syria, while acknowledging Ankara's security concerns in the volatile region.
White House National Security Council spokesman John Kirby said Turkish bombing of Kurdish-controlled areas in northeast Syria continues.
The Turkish government says it is taking military action in response to a terrorist attack in Istanbul that it blames on Kurdish groups. The Kurds deny responsibility.
"They continue to conduct airstrikes," Kirby said, adding there was no evidence yet of a threatened ground operation across the Turkish-Syrian border, where US troops deploy alongside the Kurdish-led SDF force.
Kirby said that while "Turkey does have a right to defend itself," the operations carry a heavy risk.
"We recognize their legitimate security concerns to defend themselves," he said.
"What we don't want to see are operations in Syria that, again, could cause civilian casualties, could cause casualties of our personnel and could distract our SDF partners from a very real and very important mission ongoing against ISIS," he added, using an acronym for the Islamic State group (IS).
Washington does not "want to see anything that would affect our ability to continue to put the pressure" on IS, Kirby said.
He noted that the "strategic level" of cooperation with SDF forces was not in danger.
However, Turkish offensives against the SDF meant the Kurdish forces would typically be "less willing to continue to contributing to counter ISIS" on a day-to-day basis.
"That is a concern," he said.
US-led forces resume normal patrols in Syria
A US-led coalition fighting jihadists resumed regular patrols in Kurdish-held areas of northeast Syria on Friday after earlier Turkish air strikes, an AFP correspondent and a Kurdish military source said.
Patrols were reduced following the Turkish strikes that began on November 20 in Kurdish-controlled areas of Syria and Iraq, in response to a deadly Istanbul bombing that Ankara blamed on Kurdish groups.
The Kurds denied responsibility.
Hundreds of American troops are in Syria as part of the fight against remnants of the Islamic State group.
Two four-vehicle patrols bearing US flags set off separately from a base in Rmeilan in Hasakeh province, the AFP correspondent said.
A vehicle belonging to the Kurdish-led Syrian Democratic Forces (SDF) accompanied each convoy, which travelled in different directions towards Syria's borders.
"The international coalition in cooperation with the Syrian Democratic Forces resumed its usual patrols in northeast Syria following a reduction due to Turkish strikes in the area," a Kurdish military source told AFP.
The source requested anonymity as he was not authorised to speak on the matter.
The usual 20 weekly patrols had dropped to around five or six following the Turkish strikes, which Ankara said it carried out with aircraft and drones.
The US supports the SDF, which is the Kurds' de facto army in the area and led the battle that dislodged IS from the last scraps of their Syrian territory in 2019.
Mahmud Bardakhan, a member of the SDF general command, meanwhile said the group "was forced to stop operations against IS cells for several days" due to the Turkish strikes.
But operations targeting the jihadists will resume on Saturday "in coordination with the coalition", he added.
White House National Security Council spokesman John Kirby on Friday warned Turkey not to disrupt operations by US and Kurdish forces in Syria, while acknowledging Ankara's security concerns in the volatile region.
Turkey said it struck targets of the Syrian Kurdish People's Protection Units (YPG), which dominate the SDF but which Ankara sees as an offshoot of the Kurdistan Workers' Party (PKK).
Turkey and its Western allies designate the PKK as a terrorist group.
The SDF "needs to focus on repelling the Turkish threats and protecting its areas", the Kurdish military source said.
The Syrian Observatory for Human Rights, a Britain-based war monitor with a vast network of sources on the ground, said patrols were also seen Friday in Deir Ezzor province further south.
Turkey has threatened a ground operation in the semi-autonomous Syrian Kurdish zones, something which US Defence Secretary Lloyd Austin on Wednesday expressed "strong opposition" to.
The SDF has warned that a Turkish incursion would jeopardise the fight against IS.