A Turkish fighter jet Tuesday downed a Syrian regime warplane in the northwestern Idlib province and the pilot was killed, a monitoring group said.

It was the third such downing in three days amid escalating fighting between Turkish forces and Syria's Russian- and Iranian-backed regime.

A missile fired by Syrian regime forces on the city of Idlib, meanwhile, killed nine civilians in the province of the same name that is Syria's last opposition bastion.

Syrian President Bashar al-Assad's forces have since December battled to retake the jihadist-dominated stronghold, where Ankara backs some rebel groups.

A file picture of an L-39 Albatros Syrian military aircraft of the type that was shot down Tuesday by a Turkish fighter jet over the northwestern Idlib province
A file picture of an L-39 Albatros Syrian military aircraft of the type that was shot down Tuesday by a Turkish fighter jet over the northwestern Idlib province AFP / LOUAI BESHARA

The deadly offensive has caused almost a million people to flee their homes and shelters, and triggered a direct Turkish military intervention last week.

A Turkish F-16 downed the regime plane over Idlib province, the Syrian Observatory for Human Rights war monitor and a source at the Turkish defence ministry said.

The Britain-based monitor said it was not clear if the pilot was killed during the downing or afterwards by opposition fighters, and that his body was mutilated.

Syrian state news agency SANA quoted a military source as confirming one of its planes was downed, after two others suffered the same fate on Sunday.

The Syrian conflict has killed more than 380,000 people and displaced millions since it began in 2011 with the brutal repression of anti-government protests
The Syrian conflict has killed more than 380,000 people and displaced millions since it began in 2011 with the brutal repression of anti-government protests AFP / Ibrahim YASOUF

"One of our warplanes carrying out a mission in southern Idlib... was hit by a missile fired by Turkish regime forces, leading to its downing," the source said.

The Turkish ministry said the regime plane was a L-39.

Also on Tuesday, a surface-to-surface missile fired by regime forces hit an Idlib residential neighbourhood, killing nine civilians including five children, the Observatory said.

That brings the civilian death toll since December to more than 470, according to the monitor.

Damascus meanwhile also claimed it had downed a Turkish drone near the town of Saraqeb, two days after it said it had hit three other unmanned aerial vehicles.

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

The Observatory says Turkish bombardment -- mostly drone strikes -- has killed 119 regime soldiers and 20 allied fighters since.

On Sunday, Damascus closed its air space over northwest Syria and threatening to shoot down any "enemy" aircraft violating it.

The Syrian conflict has killed more than 380,000 people and displaced millions since it began in 2011 with the brutal repression of anti-government protests.