Abu Bakr al-Baghdadi, the self-appointed caliph of a new Sunni caliphate straddling parts of Syria and Iraq, has released a video of a sermon he made at Al-Nouri Mosque in Mosul, apparently on Friday. In the video, al-Baghdadi calls on Muslims to obey him and join the caliphate.

The release of a video is a surprise. The leader of Isis rarely makes public appearances, preferring to communicate via written statements. There had also been reports circulating in recent days that he had been killed or seriously injured and had fled to Syria.

Isis, the militant Sunni terror group which has rampaged across northern Iraq for weeks, executing Shia Muslims and capturing towns, cities and oil fields, has controlled the city of Mosul for three weeks. Even so the leading of Friday prayers by al-Baghdadi, marking Ramadan, is audacious.

ISIS Crucifixion Syria
Isis is known for its brutality and holds public executions and corporal punishments Isis

In the video al-Baghdadi urges Muslims across the world to join the caliphate.

'I am the wali (leader) who presides over you,' he says, 'though I am not the best of you, so if you see that I am right, assist me. If you see that I am wrong, advise me and put me on the right track, and obey me as long as I obey God in you.'

Prior to this video's emergence only two photographs were known to exist of al-Baghdadi, one of them from his time in a US detention camp. On being handed over to Iraq forces he is reported to have told US officers, 'I'll see you in New York.'

In the new video, dressed in a black turban and robe, he cuts a very different figure to the crop-haired, besuited figure of the earlier photographs.

The creation of a caliphate by Isis – now referring to themselves as an 'Islamic State' – has been condemned by Sunni leaders across the Muslim world as being against sharia law.

Sheikh Abbas Shuman of Al-Azhar University said: 'The Islamic caliphate can't be restored by force. Occupying a country and killing half of its population... this is not an Islamic state, this is terrorism.'