Turkish and Russian military vehicles return following a joint patrol in northeast Syria, as they are pictured from near the Turkish border town of Kiziltepe in Mardin province, Nov. 1, 2019. Photo: Reuters / Kemal Aslan.

Turkey and Russia have agreed on the details of a ceasefire in Syria’s Idlib region after four days of talks in Ankara, Defense Minister Hulusi Akar said on Friday, adding that joint patrols along a key highway will begin on Sunday as planned.

Turkey and Russia, which back opposing sides in Syria’s war, agreed on March 5 to halt hostilities in the country’s northwest after a recent escalation of violence displaced nearly a million people and brought the two sides close to confrontation.

Under the agreement, Turkish and Russian forces will carry out joint patrols along the M4 highway linking Syria’s east and west, and establish a security corridor on either side of it. A Russian delegation arrived in Ankara Tuesday to work out details.

“The text that was prepared was signed by both sides and is now in effect. We will see its first application with the joint patrols on March 15,” Akar was quoted as saying by the state-run Anadolu news agency.

Akar said both Turkey and Russia were working to ensure the ceasefire becomes lasting, adding that Ankara and Moscow would establish joint coordination centers to monitor the agreement.

While the ceasefire deal addresses Turkey’s main concerns in Idlib — stopping a flow of migrants and preventing the death of more Turkish soldiers — it also cements recent gains by Russian-backed Syrian government forces and leaves Turkish observation posts in the region encircled by the Syrian side.

Akar said there were signs that migration from Idlib towards Turkish borders had stopped after the ceasefire deal. His ministry said separately talks with the Russians had concluded.

Earlier on Friday, a Turkish security official said Turkey’s observation posts in Idlib will remain in place and function despite being encircled. The official said that no heavy arms or equipment would be withdrawn from the posts.

“There are no violations (of the ceasefire) against observation posts,” which are meant to “end the bloodshed and humanitarian drama,” the official told a briefing in Ankara.

Turkey, which supports Syrian rebel groups looking to oust President Bashar al-Assad, will do “what is necessary” against any groups trying to deter the planned joint patrols, the official added.

The ceasefire deal, which has largely held since March 5, was struck after around 60 Turkish troops were killed in clashes in the region since last month.