Twin explosions in the bustling centre of the rebel-held northwestern Syrian city of Idlib on Monday killed at least 15 people and injured scores, medics and witnesses said.

Turkey is doing what is required to maintain peace and prevent violations in Syria's northern Idlib, the last major rebel stronghold in Syria, Turkey's foreign minister said on Monday.

Turkey loaded tanks and armoured vehicles onto trucks on Saturday and dispatched the convoy to the Turkish province of Hatay on the Syrian border, the Demiroren news agency said.

Turkey sent a convoy of commando units and armoured vehicles to the Turkish province of Hatay on the Syrian border, state-owned Anadolu news agency said on Friday.

Two activists critical of both the regime and jihadists were gunned down Friday in Syria's last major rebel bastion in the northwest of the country, their radio station and a monitor said.

Some militants have withdrawn from the demilitarisation zone in Idlib following a deal between Russia and Turkey on the northwestern Syrian region, a US official said on Wednesday.

Syria's army Friday warned residents of the country's last major rebel bastion to stay away from jihadists, who have yet to withdraw from a buffer zone ahead of a looming deadline.

Syrian rebels completed the withdrawal of heavy weapons from the frontline in Idlib on Monday, under the deal between Russia and Turkey to create a demilitarised zone, the state-owned Anadolu news agency said.

Syrian rebels denied on Sunday they had pulled any heavy arms from a major opposition bastion in the north, as the deadline to implement a demilitarisation deal there draws closer.

The Syrian Observatory for Human Rights said on Sunday that rebel group Failaq al-Sham has started withdrawing its forces and heavy arms from a demilitarised zone in northwest Syria.

The Syrian state will recover Idlib through war or peaceful means, a minister was quoted as saying on Tuesday, pointing to the government's determination to defeat rebels there despite a Russian-Turkish deal that halted an expected army offensive.

Turkey will take action east of the Euphrates river in Syria and impose secure zones as it has done in the northwest of the country, President Tayyip Erdogan said in comments broadcast on Turkish media on Monday.