Amnesty International on Monday condemned the US-led coalition's failure to acknowledge and investigate its role in civilian killings during the battle a year ago to oust jihadists from Syria's Raqa.

A deadline for jihadists to leave a planned buffer zone around Syria's last major rebel bastion of Idlib passed Monday without any sign they had done so, said the Syrian Observatory for Human Rights.

A planned buffer zone in northwest Syria has been cleared of heavy armaments ahead of time but a new deadline loomed Wednesday for the tougher task of Turkey convincing jihadists to pull out their fighters.

Jihadists and Turkish-backed rebels in Syria's last major opposition stronghold have withdrawn most of their heavy weapons from a planned buffer zone ahead of a Wednesday deadline, a monitor said.

The pullback is the first major test of a deal brokered by government ally Russia and rebel-backer Turkey last month to avoid what the United Nations warned would be the appalling humanitarian consequences of a major government offensive.

A Turkish military convoy entered rebel-held northwestern Syria early on Wednesday, an AFP correspondent reported, as the deadline for establishing a buffer zone between rebel and government forces draws closer.

Russia on Friday warned it will not allow jihadists in Syria to be sent to Afghanistan or elsewhere under a deal reached with Turkey that averted a large-scale military assault on rebel-held Idlib province.

Turkish troop reinforcements entered Syria's rebel bastion of Idlib on Tuesday, an AFP correspondent reported, a week after a deal between Ankara and Moscow averted a government offensive.

Around 35 military vehicles travelled south down the main highway near the town of Saraqib after midnight.

Russia's Vladimir Putin on Monday spoke to Syria's Bashar al-Assad for the first time since last week's downing of a Russian military plane, telling him of Moscow's plan to deliver a new S-300 air defense system to the Syrian army.

Israel's coordination with Russia on its attacks in Syria remains unchanged despite the deadly downing of a Russian plane, and the Jewish state retains its right to decide on military actions, an Israeli official said.

The deal to avoid a Syrian government offensive on Idlib province is still being worked out by Russia and Turkey, the UN said Thursday, stressing that the threat to civilians remained high.