Khan Sheikhun - Militants Wednesday downed a regime plane flying over northwest Syria as it took part in a deadly campaign that has seen loyalists inch forward against their opponents, a monitor said.

An AFP correspondent saw smoke rising in the south of Idlib province above the debris of the plane, with its wing bearing the Syrian flag.

After eight years of civil war in Syria, the Idlib region -- controlled by Syria’s former Al-Qaeda affiliate -- is the last major stronghold of opposition to President Bashar al-Assad’s regime.

Regime and Russian air strikes, as well as rocket fire, have pounded Idlib for more than three months, killing hundreds and displacing 400,000 people.

Over the past week, pro-Assad fighters have nibbled away at the southern edges of Idlib and on Wednesday they stood just kilometres away from a key militant -held town. The Syrian Observatory for Human Rights said Wednesday’s downing of the plane was the first such incident since late April.

“The pilot has been taken prisoner” and is in the hands of the Hayat Tahrir al-Sham (HTS) militants group running the Idlib region, Observatory head Rami Abdel Rahman said.

HTS and the correspondent said the Russian-made war plane was downed near the town of Al-Tamanaa.

The crash site lies east of the near-deserted town of Khan Sheikhun, which lies on a key highway coveted by the regime.

The road in question runs through Idlib, connecting government-held Damascus with the northern city of Aleppo, which was retaken by loyalists from rebels in December 2016.