The Syrian Democratic Forces (SDF), which is dominated by the PKK's Syrian affiliate the People's Protection Units (YPG) terrorists, shelled a Turkish base in Afrin's Mariamin village with mortars late Tuesday, according to local sources.
No casualties have yet been reported.
Some skirmishes between the YPG and Turkish forces were also reported on Serekaniye border, near the border town of Ras al-Ain.
Ankara has been sending more armored vehicles to the border with Syria as it prepares to launch its third cross-border anti-terror operation, this time to clear the area to finally set up a safe zone for Syrians. Dozens of vehicles were seen moving in a large convoy in the Turkish town of Akçakale in Şanlıurfa province.
Different types of construction equipment were also part of the convoy which had been sent to reinforce the military units on the border, state news agency Anadolu reported.
The Turkish Defense Ministry earlier said preparations for the military operation in northern Syria against the U.S.-backed YPG militia were "completed".
President Recep Tayyip Erdoğan has repeatedly threatened to launch an offensive against and said Monday that Turkey could start the operation "without warning".
Since 2016, Turkey's Euphrates Shield and Olive Branch operations in northwestern Syria have liberated the region from the YPG/PKK and Daesh terrorists, making it possible for Syrians who fled the violence to return home.
Turkey has long decried the threat from terrorists east of the Euphrates River in northern Syria, pledging military action to prevent the formation of a "terrorist corridor" there.