The US has pressed Turkey to halt military strikes on Kurdish and Syrian regime targets in the northern province of Aleppo, as Ankara weighs a joint ground assault with Saudi troops.
"We are concerned about the situation north of Aleppo and are working to de-escalate tensions on all sides," State Department spokesman John Kirby said in a statement on Friday.
State-run news agency Anatolia, quoting a military source, said the armed forces shelled Syrian Kurdish Democratic Union Party (PYD) targets around the town of Azaz, and also responded to regime fire on a Turkish military guard post in Turkey’s southern Hatay region.
There were no further details on the nature of the Turkish strikes, but they likely would involve artillery fire from tanks.
"We have urged Syrian Kurdish and other forces affiliated with the YPG not to take advantage of a confused situation by seizing new territory," Kirby said.
"We have also seen reports of artillery fire from the Turkish side of the border and urged Turkey to cease such fires."
The Syrian Observatory for Human Rights said Minnigh air base, recently taken by the Kurdish People’s Protection Units (YPG) militia from Islamist rebels, was hit in the Turkish shelling.
Ankara considers the PYD and its YPG militia to be branches of the Kurdistan Workers Party (PKK) which has waged a decades-long insurgency against the Turkish state.
"Turkey and the YPG share a serious threat of ISIL poised just to the east of the Azaz corridor," Kirby added, referring to the self-proclaimed Islamic State group that has seized territory in Syria and Iraq.
"We continue to encourage all parties to focus on this common threat, which has not subsided, and to work toward a cessation of hostilities, as agreed in Munich."
The shelling came just a day after world powers announced announced an ambitious plan to stop fighting in Syria within a week.
But doubts have emerged over its viability, especially because it did not include IS or Al-Qaeda’s local branch, which is fighting alongside other rebel groups in several areas.