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

Turkey supported opposition groups seeking to overthrow Bashar Assad’s regime, while Russia helped consolidate Assad after a decade of conflict.

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

“The main item on the agenda is Syria, namely Idlib,” a senior Turkish official said, speaking on condition of anonymity, of the talks scheduled for the Russian resort of Sochi. “The conditions set out in the Idlib deal have not been fully implemented.”

The March 2020 deal follows weeks of fighting that brought Turkey and Russia closer to conflict and displaced nearly a million people.

“There should be no further 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, officials said, without specifying exact dates.

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

NATO member Turkey has purchased Russian S-400 air defenses, resulting in US sanctions against Turkish defense industries, and is in talks with Russia to possibly purchase a second batch.

The two Turkish officials said this would be discussed, along with energy projects and tourism.

Ankara and Moscow were rivals in Nagorno-Karabakh in fighting between Azerbaijani and Armenian forces last year. While Russia has negotiated a ceasefire 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 in the Donbass region, and later to Poland in the first such sale to a member of NATO.

The official said Nagorno-Karabakh and drone sales would be discussed in Sochi, while the senior official said continued defense cooperation could be discussed.