Turkish President Recep Tayyip Erdoğan is expected to visit Russia later this month for talks with President Vladimir Putin about the violence in northwestern Syria, where Moscow and Ankara back opposing sides, two Turkish officials said on Friday.

Turkey has backed opposition groups who sought to topple Bashar Assad regime, while Russia has helped shore up Assad after a decade of conflict.

Both sides have complained about violations of a truce they agreed on 18 months ago in the northwestern Idlib region, the last opposition bastion left in Syria, where Ankara says two Turkish troops were killed in an attack on Saturday.

"The main agenda point is Syria, namely Idlib," a senior Turkish official, speaking on condition of anonymity, said of the planned talks in the Russian resort of Sochi. "The conditions set out in the Idlib agreement have not been fully implemented."

The March 2020 agreement followed weeks of fighting that brought Turkey and Russia close to conflict and displaced nearly a million people.

"There should not be any new instability in Syria," another Turkish official told Reuters.

Erdoğan's planned two-day visit will follow his trip to the United Nations General Assembly (UNGA) in New York next week, the officials said, without specifying the exact dates.

Despite backing opposing sides in both the Syrian and Libyan conflicts, Turkey and Russia have forged close cooperation in the defense, energy and tourism sectors.

NATO member Turkey has bought Russian S-400 air defenses, leading to U.S. sanctions on Turkish defense industries, and has been in talks with Russia over possibly buying a second batch.

Both Turkish officials said this would be discussed, as well as energy projects and tourism.

Ankara and Moscow were rivals in Nagorno-Karabakh during fighting between Azerbaijani and Armenian forces last year. While Russia brokered a cease-fire between Turkey-backed Azerbaijan and Armenia, it is working with Ankara to monitor it.

Turkey also angered Russia earlier this year when it sold Turkish drones to Ukraine amid tensions over the Donbass region, and later to Poland in the first such sale to a NATO member.

The official said both Nagorno-Karabakh and the drone sales would be discussed in Sochi, while the senior official said that further defense cooperation may be discussed.