Several Islamic State (Isis) fighters who fled Ramadi after losing the key city to Iraqi troops have reportedly been burned alive by the terror group.

Residents in Mosul, some 400km north of Ramadi city said signature Daesh black-clad jihadists set fire to the fighters in the town's main square for not fighting to the death.

"They were grouped together and made to stand in a circle and set on fire to die," a former resident of Iraq living in US in contact with a family in Mosul told FoxNews. Some Isis fighters met a similar fate in 2015 when they gave up fighting for the city of Tikrit.

Sajad Jiyad, an Iraq analyst, had earlier told the Financial Times of an incident in which the city was retaken in December after Iraqi forces entered a complex in the city and did not face any opposition from Isis, indicating that the Islamist fighters withdrew to the north-east of Ramadi when they realised it had fallen.

Reports have also emerged of women and children being killed by the group on suspicion of being spies. Clint Watts, Fox fellow of the Foreign Policy Research Institute, says: "As Isis continues to lose territory, we've seen a growing number of defections and a rise in the number of alleged internal spies – many of whom they have killed mercilessly without demonstrating significant evidence of internal espionage."

The recapture of Ramadi is a big blow to Isis and a major success for Iraq's army. Iraq's government, which has pledged to make its territories Isis-free in 2016, has declared that its next target for liberation will be Mosul, by far the most heavily populated city controlled by Isis in either Iraq or Syria.