An Islamic State drone filmed itself dropping a bomb which set off a chain of huge explosions at an ammunition dump inside a stadium in Syria.

Islamic State's propaganda arm Amaq released the footage of the attack near the town of Deir Ezzor, where Syrian government forces have been fighting with IS for control since September.

It shows a bomb falling away from the drone and an initial small explosion which appears to set off a chain of larger blasts.

Government forces captured a military airport south of the stadium on September 9.

IS had lost ground in Syria in recent weeks.

The group's de facto Syrian capital of Raqqa was declared liberated on October 17, when US-backed forces raised a flag inside Raqqa stadium.

The loss is seen as hugely symbolic for the group, as Raqqa was the first large Syrian city to come under rebel control in March 2013.

Iraq prepares for final offensive

Iraqi forces are about to launch an offensive to recapture the last patch of Iraqi territory still in the hands of Islamic State, the military there said.

"Your security forces are now coming to liberate you," said leaflets dropped by the Iraqi air force on the western border region of Al Qaim and Rawa, according to a statement from the Joint Operations Command in Baghdad.

The militant group also holds parts of the Syrian side of the border, but the area under their control is shrinking as they retreat in the face of a US-backed, Kurdish-led coalition and Syrian government troops with foreign Shiite militias backed by Iran and Russia.

IS's self-declared cross-border caliphate effectively collapsed in July, when US-backed Iraqi forces captured Mosul — the group's de facto capital in Iraq — in a gruelling battle lasting nine months.

IS leader Abu Bakr al-Baghdadi, who declared the caliphate from Mosul in mid-2014, released an audio recording on September 28 that indicated he was alive, after several reports he had been killed.

He urged his followers to keep up the fight despite setbacks.

"God is with us in this last assault on Daesh members," the Iraqi leaflets said, using another name for IS.

Sorry, this video has expired Iraqi Federal Police celebrate in the Old City of Mosul.

ABC/ Reuters