Militants fighting for the Islamic State (Isis) have executed their own members by locking them in cars and filling them with toxic gas, as punishment for fleeing the battlefield, according to reports on 9 August.

The incident was said to have taken place in northern Iraq near its stronghold of Mosul, the country's second city. Fighters were thought to have had their hands and feet bound before being thrown into a car where they were gassed to death., for not willingly fighting to the death.

Independent online news organisation, the American Herald Tribune (AHT), quoted Arabic-language websites in its report. However, the report has not been independently verified by IBTimes UK.

"IS (Daesh) tied up hands and feet of its militants, put them inside a closed-door car with all the windows rolled up and opened gas hose sent into the car until they died," AHT said.

Similar examples of senior IS commanders executing their own men have been reported in the last few months, including reportedly boiling them alive in water. The jihadists in this latest instance were said to have fled the battlefield in al-Shirqat in the Iraqi province of Salahuddin.

The city of Mosul was overrun by IS militants in June 2014 and despite remaining under IS control, many of the the group gains have since been clawed back by the Iraqi army backed by US-led coalition air strikes and Kurdish forces.

The report comes just days after a mass grave was discovered containing the bodies of 200 Isis extremists on Khalediya Island, on the Euphrates, in Iraq's Anbar province. The grave was found on the Island on 6 August after the area was liberated by the Iraqi army as they head north.

After liberating Ramadi and Fallujah the Iraqi Army have now set their sights on liberating Mosul. The Iraqi army has taken up positions around the city, 248 miles north of Baghdad, with US President Barack Obama saying that he expects the city to fall at some point in 2016.