Islamic State group supporters and a monitoring group said militants shot down a government helicopter in northern Syria early on Sunday.

The Syrian Observatory for Human Rights said IS had brought down the helicopter after midnight near the Kweyris air base in the east of Aleppo province.

Observatory director Rami Abdel Rahman said at least one crew member had been killed but "the fate of the rest is unknown".

Militant accounts on Twitter said IS had shot down the helicopter using anti-aircraft missiles.

They posted the names of three crew members they said had been killed and posted pictures of a helicopter in flames.

But Syrian state television said the aircraft had crashed because of technical problems.

"A helicopter crashed after takeoff from Kweyris airport in Aleppo province because of technical faults and the crew were killed," it reported.

IS fighters have surrounded the air base since March 2014 and have fought fierce clashes with its garrison.

The Syrian government has used helicopters to drop barrel bombs on rebel-held areas of Aleppo province.

The crude weapons - made from oil drums, gas cylinders or water tanks, packed with explosives and scrap metal - have killed hundreds of civilians, drawing condemnation from human rights groups.

President Bashar al-Assad has denied they are being used.