In the Ras al-Ain border region, an AFP correspondent heard loud explosions and saw clouds of white smoke towering overhead.

The journalist said Turkish artillery fire also hit the region, adding that he saw dozens of civilians flee in cars and on motorbikes.

The Syrian Observatory for Human Rights war monitor said "air strikes" and "artillery fire" hit Ras al-Ain and the surrounding area.

Turkish artillery fire also hit several villages in the Tal Abyad border region, to the west of Ras al-Ain, according to the Britain-based Observatory.

The Syrian Democratic Forces, a Kurdish militia that controls most of northeastern Syria, confirmed the reports, saying that "Turkish warplanes have started to carry out air strikes."

"There is a huge panic among people of the region," spokesman Mustefa Bali wrote on Twitter.