Pro-Syrian regime militias entered the northwestern Afrin region on Tuesday, pitting them against Turkish forces fighting the Kurdish People’s Protection Units (YPG). The confrontation pits the Turkish army and allied Syrian rebel groups directly against the military alliance backing the regime of Bashar Assad, further scrambling northwest Syria’s already messy battlefield. Soon after the convoy of militia fighters - waving Syrian flags and brandishing weapons - entered Afrin, Syrian state media reported that Turkey had targeted them with shellfire. Turkish President Recep Tayyip Erdogan described the convoy as being made up of “terrorists” acting independently. He said Turkish artillery fire had forced it to turn back, although the YPG denied this. Ankara’s month-old offensive is aimed at driving the YPG, which it sees as a big security threat on its border, from Afrin. In a statement on Tuesday, YPG spokesman Nuri Mahmud said the Kurdish forces had called on Damascus to help fend off Turkeys assault. "The Syrian regime 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. AFP correspondents said the forces did not appear to have entered Afrin city itself. The YPG said they were deploying along the front line facing the Turkish border. Erdogan said he had previously reached an agreement with Russian President Vladimir Putin and Iran’s President Hassan Rouhani, Assad’s main international backers, to block Syrian regime support for the YPG fighters. YPG media adviser Rezan Hedo denied Erdogan’s assertion that the convoy had turned back under Turkish artillery fire, but he gave no details on its size or composition. A Britain-based monitoring group, the Syrian Observatory for Human Rights, said one convoy had entered Afrin while another turned back. Earlier on Tuesday, Erdogan said he had received Putin’s agreement to block a Syrian regime deployment in Afrin. Russian Foreign Minister Sergei Lavrov said on Monday the Afrin crisis could be resolved through direct negotiations between Damascus and Ankara.