World Bulletin/News Desk

The leader of the militant organization Islamic State of Iraq and the Levant appeared in what would be his first video appearance, according to a video published Saturday on a website linked with the militant group.

The video, whose authenticity has not been independently verified, captures Abu Bakr al-Baghdadi -- the self-styled "Caliph" of the self-declared Islamic state established in an area straddling Iraq and Syria -- preaching during Friday prayer at a mosque in Mosul.

"Allah gave me a big responsibility and a noble command," the man purported to be Baghdadi is saying in the video.

"I am not promising wealth and luxury like kings to my subjects, but I am promising what Allah promises to his faithful servants," he says.

On Monday, ISIL announced the establishment of an Islamic state in the region led by Baghdadi.

The move has been widely condemned in the Islamic world, with International Union of Muslim Scholars saying the declaration of the caliphate contravened "Islamic principles and the actual conditions."

Iraq saw a significant increase in sectarian violence between Sunni and Shia Muslims in June, with a coalition of armed opposition groups led by the ISIL taking control of large swathes of the country's predominantly Sunni provinces.

The latest wave of insurgency began when militants captured the city of Mosul on 10 June and soon afterwards took control of a number of other key cities and towns including Tikrit, Tal Afar, Fallujah and Baiji.

The Iraqi government denied that the 21-minute video, which carried Friday's date, was credible.

"We have analysed the footage ... and found it is a farce," Interior Ministry spokesman Saad Maan told Reuters.

Maan said government forces had recently wounded Baghdadi in an air strike and that he had been transferred by Islamic State militants to Syria for medical treatment. But he declined to give further details and there was no way to confirm the claim independently.

The video was shared widely on social media, and some residents of Mosul told Reuters on Saturday that they had witnessed a man introduced to them as Baghdadi preaching in a mosque in the centre of the city on Friday.

The three witnesses said the man had entered the mosque flanked by gunmen wearing uniforms worn by Islamic State militants.

"We held our breath out of fear and surprise," said one worshipper who spoke on condition of anonymity.

Another eyewitness said: "A man from the group started to speak to us in a loud tone in eloquent Arabic saying that Ameer al-Mumineen (Prince of Believers) Abu Bakr al-Baghdadi is here to give Friday's speech, and he asked everybody not to use mobiles to take photos or film, for security reasons."

A third worshipper added: "The speech lasted for around 20 minutes, then the man wearing black who was introduced to us as al-Baghdadi took the lead in the Friday prayer and then, after finishing, he left with dozens of his followers in a long motorcade."