'The Turkish army has attacked pro-Syrian government forces that had earlier arrived in the Kurdish-held Afrin region in northwestern Syria to defend the Syrian Kurds against Turkey’s offensive.
"Turkish regime forces targeted the locations of popular forces with artillery fire as they arrived to the Afrin region," Syria’s state news agency SANA reported on Tuesday.
On Tuesday afternoon, hundreds of popular forces from the National Defense Forces (NDF) supporting the government in Damascus began entering the Kurdish-held region of Afrin through the al-Ziyara crossing point north of the town of Nubl.
Turkish state news agency Anadolu said Turkey’s army fired "warning shots" at the Syrian popular forces, noting that they “retreated to about 10 kilometers from the town because of the warning shots."
The shelling marks a major escalation of tensions between the two countries since Turkey and its allied militants launched a military offensive against Afrin last month.
In a statement on Tuesday, US-backed People's Protection Units (YPG) spokesman Nouri Mahmoud said the Kurdish forces had called on the Syrian government to help fend off Turkey's assault.
"The Syrian government responded to the invitation, answered the call of duty and sent military units today, February 20, to take up positions on the borders, and participate in defending the territorial unity of Syria and its borders," the statement said.'
Read more: Turkish army shells pro-Syrian government forces as they enter Afrin