Turkish and Russian officials have largely agreed on details of a ceasefire deal in Syria's war-battered Idlib province, Turkish Defence Minister Hulusi Akar said on Thursday, the third day of discussions between the two countries.

Last week, NATO-member Turkey and Russia - the two countries back opposing sides in Syria's war - agreed on the ceasefire to halt an escalation of violence in Idlib that has displaced nearly a million people and brought the two countries close to direct confrontation.

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Under the agreement, Turkish and Russian forces will carry out joint patrols along the strategic M4 highway linking Syria's east and west, and establish a security corridor either side of it.

A Russian delegation arrived in Ankara this week to discuss the details of the agreement.

The corridor stretches 6km (3.7 miles) to the north and 6km to the south of the M4 - effectively advancing Russia's presence further north into Idlib.

The security corridor stretches 6km (3.7 miles) to the north and 6km to the south of the M4 highway [ Omar Haj Kadour/AFP]

Russia supports Syrian President Bashar al-Assad, while Turkey backs opposition factions who have fought him for nearly nine years.

"We have largely reached an agreement. At the moment, the attacks have stopped, the ceasefire is holding," Akar was cited as saying by his office. "The joint patrols will start along the M4 on March 15. Our colleagues are discussing the details of that."

A senior Turkish official told Reuters news agency that concrete results were expected from the discussions in Ankara. Turkey was prepared to retaliate against violations by the Syrian government, he added.

"The fact that we are moving in line with the agreements brings hope for the future. We are moving forward," the official said, speaking on condition of anonymity.

Fragile ceasefire

On Wednesday, President Recep Tayyip Erdogan said Turkey would not shy away from even stronger military action in Idlib if the ceasefire is broken.

Akar also said on Thursday that all Turkish forces remained in their positions in Idlib.

The latest Russia-backed offensive in Idlib by al-Assad's forces sparked what the United Nations says may be the worst humanitarian crisis yet in a war that has driven millions from their homes and killed hundreds of thousands.

Russia had repeatedly played down any talk of a refugee crisis and accused Turkey of violating international law by pouring troops and equipment into Idlib since early last month.

About 60 Turkish troops have been killed in that time.