BAGHDAD (AP) — A man purporting to be the leader of the Sunni extremist group that has declared an Islamic state in territory it controls in Iraq and Syria has made what would be his first public appearance, delivering a sermon at a mosque in Iraq’s second-largest city, according to a video posted online Saturday.

The 21-minute video that is said to show Abu Bakr al-Baghdadi, the head of the Islamic State group, was reportedly filmed on Friday at the Great Mosque in the northern city of Mosul. It was released on at least two websites known to be used by the organization and bore the logo of its media arm, but it was not possible to independently verify whether the person shown was indeed al-Baghdadi.

There are only a few known photographs of al-Baghdadi, an ambitious Iraqi militant believed to be in his early 40s with a $10 million U.S. bounty on his head. Since taking the reins of the group in 2010, he has transformed it from a local branch of al-Qaida into an independent transnational military force, positioning himself as perhaps the pre-eminent figure in the global jihadi community.

Al-Baghdadi’s purported appearance in Mosul, a city of some 2 million that the militants seized last month, came five days after his group declared the establishment of an Islamic state, or caliphate, in the territories it seized in Iraq and Syria. The group proclaimed al-Baghdadi the leader of its state and demanded that all Muslims pledge allegiance to him.

In the video, the man said to be al-Baghdadi says that “the mujahedeen have been rewarded victory by God after years of jihad, and they were able to achieve their aim and hurried to announce the caliphate and choose the Imam,” referring to the leader.

“It is a burden to accept this responsibility to be in charge of you,” he adds. “I am not better than you or more virtuous than you. If you see me on the right path, help me. If you see me on the wrong path, advise me and halt me. And obey me as far as I obey God.”

Speaking in classical Arabic with little emotion, he outlines a vision that emphasizes holy war, the implementation of a strict interpretation of Islamic law, and the philosophy that the establishment of an Islamic caliphate is a duty incumbent on all Muslims.

He is dressed in black robes and a black turban — a sign that he claims descent from the Prophet Muhammad. He has dark eyes, thick eyebrows and a full black beard with streaks of gray on the sides.

At the beginning of the video, the man purported to be al-Baghdadi slowly climbs the mosque’s pulpit one step at a time. Then the call to prayer is made as he cleans his teeth with a miswak, a special type of stick that devout Muslims use to clean their teeth and freshen their breath.

The camera pans away at one point to show several dozen men and boys standing for prayer in the mosque, and a black flag of the Islamic State group hangs along one wall. One man stands guard, with a gun holster under his arm.

Aymenn al-Tamimi, an expert on militant factions in Syria and Iraq, said al-Baghdadi has come under some criticism since unilaterally declaring the establishment of a caliphate, in part for not appearing before the people.

“He had declared himself caliph, he couldn’t hide away. He had to make an appearance at some time,” al-Tamimi said. Traditionally, a Muslim ruler is expected to live among the people, and to preach the sermon before communal Friday prayers.

The brazenness of his purported appearance — nearly unheard of among the most prominent global jihad figures — before dozens of people, and issued on a video only a day after its occurrence, suggested the Islamic State’s confidence in their rule of Mosul.

“The fact that he has done this without any consequences in Mosul’s biggest mosque is a sign of (the Islamic State group’s) power within the city,” said al-Tamimi. He said it would likely boost the morale of al-Baghdadi’s fighters, and deal a blow to the group’s rivals.

A senior Iraqi intelligence official said that after an initial analysis the man in the video is believed to indeed be al-Baghdadi. The official said the arrival of a large convoy in Mosul around midday Friday coincided with the blocking of cellular networks in the area. He says the cellular signal returned after the convoy departed.

The official spoke on condition of anonymity because he was not authorized to brief the media.

A Mosul resident confirmed that mobile networks were down around the time of Friday prayers, and then returned a few hours later. He spoke on condition of anonymity because of fears for his safety.

Another aspect of the rule al-Baghdadi envisions was made clear in a series of images that emerged online late Saturday showing the destruction of at least 10 ancient shrines and Shiite mosques in territory his group controls.

The 21 photographs posted on a website that frequently carries official statements from the Islamic State extremist group document the destruction in Mosul and the town of Tal Afar. Some of the photos show bulldozers plowing through walls, while others show explosives demolishing the buildings in a cloud of smoke and rubble.

Residents from both Mosul and Tal Afar confirmed the destruction of the sites.

Sunni extremists consider Shiites Muslims heretics, and the veneration of saints apostasy.

Also Saturday, Iraqi Prime Minister Nouri al-Maliki removed the chief of the army’s ground forces and the head of the federal police from their posts as part of his promised shake-up in the security forces following their near collapse in the face of the militant surge.

Military spokesman Lt. Gen. Qassim al-Moussawi said al-Maliki signed the papers to retire Lt. Gen. Ali Ghaidan, commander of the army’s ground forces, and Lt. Gen. Mohsen al-Kaabi, the chief of the federal police. Al-Moussawi said both men leave their jobs with their pensions. No replacements have been named.

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