The presidents of Russia and Turkey said on Monday they had agreed to create a "demilitarised zone" around Syria's Idlib, in a move aimed at preventing a military assault on the rebel-held province.

"We have decided to create a demilitarised zone some 15 to 20 kilometres deep along the line of contact between the armed opposition and regime troops by October 15 of this year," President Vladimir Putin said after more than four hours of talks with his Turkish counterpart Recep Tayyip Erdogan.

This would entail a "withdrawal of all radical fighters" from Idlib including the Al-Nusra Front, Putin said.

The two leaders also agreed on the withdrawal of "heavy weaponry from this zone," including tanks, multiple launch rocket systems, and rocket launchers belonging to all armed groups, Putin added.

"Control in the demilitarised zone will be organised together with mobile patrol groups of Turkish contingents and contingents of Russian military police," he said.

By the end of the year, transportation routes between Latakia and Aleppo as well as Latakia and Hama must be restored, Putin added.

Erdogan said the measures would "prevent a humanitarian crisis".

Russian Defence Minister Sergei Shoigu said that the agreement between Putin and Erdogan meant that no military action would be taken against Idlib, Russian news agencies reported.

Russia-backed forces of the Syrian regime have massed around Idlib province in recent weeks.

That sparked fears of an imminent air and ground attack to retake the last major opposition bastion.