Iraqi officials are investigating the authenticity of a video purportedly showing the leader of the Islamic State group which has seized large areas of the country delivering a sermon, authorities have said.

Iraqi military spokesman Qassim al-Moussawi on Sunday said the country's security services were still analysing the video to verify whether the speaker was indeed Abu Bakr al-Baghdadi, the head of the group formerly known as the Islamic State of Iraq and the Levant (ISIL) which has now rebranded itself as the Islamic State.

Moussawi said that the government would "announce the details once they are available".

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They were trying to determine if the 21-minute video said to show Baghdadi filmed on Friday at the Great Mosque in the northern city of Mosul was real.

The footage was released on at least two websites known to be used by the organisation and bore the logo of its media arm.

The video came five days after Baghdadi's group declared the establishment of an Islamic state, or caliphate, in the territories it had seized in Iraq and Syria.

The group proclaimed Baghdadi the leader of its state and demanded that all Muslims pledge allegiance to him.

Initial analysis

Wearing black robes and a black turban, the man in the video said to be Baghdadi urged his followers to follow him in the war against his enemies.

A senior Iraqi intelligence official told AP on Saturday that an initial analysis indicated that the man in the video was indeed Baghdadi. 

Over the past month, Baghdadi's fighters have overrun much of northern and western Iraq, adding to the territory they already control in neighbouring Syria. 

One of the main battlefronts now is the country's largest oil refinery near Beiji, some 250km north of Baghdad, where government forces are besieged by Islamic State group fighters.

The military spokesman said that security forces repelled an overnight attack on the facility, killing about 20 fighters and damaging eight vehicles.

Source: AP