Turkey warned that the advances by Russian-backed Syrian regime forces and their allies threaten a fresh humanitarian disaster in Syria's northwestern Idlib province.
Turkey reinforced its military presence in Syria's northwestern Idlib province on Saturday as Turkish and Russian officials held talks about the Syrian regime offensive there, which has displaced more than half a million people in two months.
Turkey says the advances by Russian-backed Syrian regime forces and their allies threaten a fresh humanitarian disaster, driving another wave of potential refugees to its southern border, and has threatened to act if they do not pull back.
Witnesses at the border said convoys of Turkish military vehicles had been crossing into Idlib since Friday, delivering supplies before turning back to return with more.
In Ankara, officials from Turkey and Russia held three hours of apparently inconclusive talks, agreeing to meet again next week.
"The situation in Idlib was discussed," Turkey's foreign ministry said after the talks. "Steps that could be taken to establish peace on the ground as soon as possible and advance the political process were evaluated."
In September 2018, Turkey and Russia agreed to turn Idlib into a de-escalation zone in which acts of aggression are expressly prohibited.
But more than 1,800 civilians there have been killed in attacks by regime and Russian forces since then, flouting both the 2018 cease-fire and a new one that started on January 12
More than 1.7 million Syrians have moved near the Turkish border due to intense attacks over the past year.
Turkey remains the country with most refugees in the world, hosting more than 3.7 million Syrians since the start of the Syrian civil war.
Turkish President Recep Tayyip Erdogan threatened this week to repel the Russian-backed Syrian regime forces unless they withdraw from the region by the end of the month.
Regime forces have pressed their advances, surrounding several Turkish observation posts.
On Monday, an Assad regime attack in Idlib killed seven Turkish soldiers and one civilian contractor working with the Turkish military, and injured over a dozen people.
"Our checkpoints in Idlib continue their duties as usual and are capable of protecting themselves," Turkey's Defence Ministry said, adding they would respond to any new attack "in the harshest manner in accordance with legitimate defence".
The Syrian Observatory for Human Rights, a UK-based war monitor, said on Saturday that 430 Turkish military vehicles had crossed into Idlib in the last 24 hours.
Turkish forces were setting up a new post at Al Mastoumah, on the southern approach to Idlib city, the Observatory said.
Syrian state TV broadcast live on Saturday from the strategic town of Saraqeb, located at the junction of the two main highways in Idlib that Assad seeks full control of, and lies less than 15 km (10 miles) southeast of Idlib city.