It is unclear when the footage was filmed, but the man said to be Baghdadi referred in the past tense to the months-long fight for Baghouz, IS's final bastion in eastern Syria, which ended last month.

"The battle for Baghouz is over," the man said, sitting cross-legged on a cushion and addressing three men whose faces have been blurred.

But he insisted that IS's operations against the West were part of a "long battle," and that IS would "take revenge" on members who had been killed.

"There will be more to come after this battle," he said.

Baghdadi, 47, had a long grey beard that appeared dyed with henna and spoke slowly, often pausing for several seconds in the middle of his sentences.

He appeared for the first and last time in public in Mosul in 2014, where he declared an Islamic "caliphate" in the swathes of territory IS then held in Syria and Iraq.

He was reported killed or injured multiple times since then.

His last voice recording to his supporters was released in August, eight months after Iraq announced it had defeated IS and as US-backed forces closed in next door in Syria.