Turkey on Sunday confirmed it had launched a military operation against Russia-backed regime forces in the border region, where Ankara supports some rebel groups.

Syrian state news agency SANA said one of its planes was "targeted" after two others were shot down on Sunday.

Turkey confirmed the downing of an L-39 jet.

"As part of the Spring Shield operation that is successfully continuing, an L-39 plane belonging to the regime has been downed," the Turkish defence ministry said.

The Observatory said the regime plane was brought down by a Turkish F-16 and crashed to the ground in a regime-held area south of the embattled rebel bastion.

The fate of the crew was not immediately clear, the Britain-based Observatory said.

Regime forces have since December been battling to retake the last major opposition bastion of Idlib from rebels and jihadists linked to Syria's former Al-Qaeda affiliate.

The Turkish operation came after an air strike on Thursday blamed on Damascus killed 34 Turkish soldiers in the region.

The Observatory says 93 regime soldiers have been killed in Turkish bombardment since Friday along with 10 fighters of the Lebanese Shiite movement Hezbollah and four pro-Iranian fighters.

On Sunday, Damascus claimed to have brought down three Turkish drones over the region.

The Syrian conflict has killed more than 380,000 people since it began in 2011 and displaced millions.