The leader of the self-proclaimed Islamic State of Iraq and Sham (ISIS) militants 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, ISIS 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."