The Syrian military and allied Shiite militiamen have advanced into the southwestern province of Quinetra as Russian jets have stepped up their bombing of an ISIS enclave near the Jordanian-Israeli border.
The Yarmouk Basin, which lies near the Israeli-occupied Golan Heights, is holding around 1,000 ISIS fighters who have repelled a Syrian military ground attack.
The army and its allies have been pushing to expand their foothold near the Golan frontier by negotiating surrender deals with rebel groups and allowing them to move to opposition-held areas in northern Syria. ISIS-affiliated fighters have attempted to push into the areas abandoned by the rebels.
Displaced people in a convoy of around 50 buses being transported from Quneitra to northwestern province of Idlib have said that Shiite militiamen allied to the Syrian regime have held them for hours south of the central city of Homs. The convoy left late Saturday night.
State news agency Sana published images of white buses it said were leaving Quneitra's Umm Batna area on the ceasefire line, watched by men in military uniform.
In neighbouring Deraa province, 19 buses carrying rebels and civilians hit the road north, more than half from the town of Nawa, the UK-based Syrian Observatory for Human Rights (SOHR) said.
An earlier convoy of hundreds of rebel fighters ands their families arrived at the Morek crossing to Idlib in northwestern Syria. The evacuations from Quneitra province came after a Russia-brokered agreement struck earlier this week for rebels to cede the territory to the Syrian regime.
Just over a month into a Russia-backed regime campaign to retake Daraa and Quneitra from rebels, Moscow-brokered surrender deals are paving the way for government institutions to return to nearly all parts of these provinces.
The deals provide for rebels who do not agree to a government takeover to board buses with their families to join other opposition fighters in the north of the country.
The US State Department said on Tuesday that Secretary of State Mike Pompeo spoke with his Russian counterpart Sergei Lavrov a day earlier about the situation in southern Syria.
"Among the topics discussed was the fact that Russia had violated its commitment in southwest Syria," spokesperson Heather Nauert said in a statement, without elaborating.
Last month, Russia carried out air strikes in the area in defiance of a ceasefire agreement with the US and Jordan that held for almost a year with a view to preserving the status quo in the area. Washington has consistently criticised Moscow and Damascus for its entry into the "de-escalation zone" but it appears that the threat of a US retaliation is diminishing.
Elsewhere in Syria, Russia's military said it had shot down two unidentified drones that attacked its Syrian air base at Hmeimim on Saturday and Sunday, Russian agencies reported.
The attacks caused no casualties or damage and the Hmeimim air base is operating as normal, Interfax said.