The leader of an Islamist militant group that has seized control of territory from Syria to Iraq made a rare public appearance last week, urging his followers and other Muslims to use the holy month of Ramadan to escalate their jihad against “the enemies of God,” according to a video posted online Saturday.

Abu Bakr al-Baghdadi, the self-declared leader of the al-Qaeda-inspired Islamic State, which declared the restoration of the medieval Muslim caliphate in parts of Iraq and Syria last week, is purportedly shown in the video preaching to followers Friday at a mosque in the northern Iraqi city of Mosul.

The SITE Intelligence group, which tracks extremist movements and statements, confirmed Baghdadi’s appearance in the video, which identifies him as “Caliph Ibrahim.” Baghdadi is a nom de guerre. He is also known as Ibrahim al-Samarrai. The video, published by the Islamic State’s media wing, would be the first that Baghdadi has made, as well as marking one of the few instances that the reclusive leader has appeared in public.

The man in the video closely resembles a photo of Baghdadi released by Iraq’s Interior Ministry in January, but with a fuller beard.

Last month, the Islamic State in Iraq and Syria, which now calls itself the Islamic State, seized control of a vast swath of northern and western Iraq, routing Iraqi forces and coming within 50 miles of Baghdad.

Iraq’s military has struggled to repel the extremists, who seized caches of advanced weaponry and vehicles from the Iraqi military during their lightning takeover of Mosul in June. Advancing across the country, the Sunni militants have found allies among other jihadist groups, as well as ordinary Iraqi Sunnis who have felt marginalized by Iraq’s Shiite-dominated government.

Earlier Saturday, a high-ranking Western diplomat in Baghdad described the Islamic State as “well-trained, hard-core terrorists.”

“It’s a real world-class terrorist organization, and it’s an army,” said the diplomat, who spoke on the condition of anonymity in accordance with embassy protocol. “They have to be isolated, squeezed off, and captured or killed.”

The Islamic State seeks to impose an extremist interpretation of Islamic law and has vowed to destroy the Iraqi government and Shiite holy sites. An official in the prime minister’s office said Saturday night that the government had no official reaction to the video.

“As of yet, we haven’t confirmed that that is, in fact, Abu Bakr al-Baghdadi,” said the official, Ali Malawi.

Last month, the Islamic State published photos purportedly documenting the gruesome execution of dozens of Iraqi Shiite soldiers and claimed to have executed 1,700 of them. Human Rights Watch said last month that the Sunni militants had executed at least 160 people in the northern city of Tikrit alone.

In 2011, the State Department identified Baghdadi as the leader of al-Qaeda in Iraq and labeled him a specially designated global terrorist. The U.S. government has offered a $10 million reward for information on his whereabouts.

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In the video, the man purported to be Baghdadi addresses rows of ordinary-looking men and boys from a podium in Mosul’s Great Mosque, telling them he is “not better” than they are. Black-clad fighters stand among the worshipers, shouldering assault rifles.

Ramadan, which entered its seventh day Saturday, is the month in the Islamic calendar when Muslims believe God delivered the Koran to the prophet Muhammad.

It is also the month when Muhammad “gathered the armies to fight the enemies of God, to fight the heathens,” Baghdadi says in the video, in which he is shown wearing black clothes and a black turban. “Take the opportunity provided by this month, oh believers. Obey God. God’s appreciation will be double this month.”

Islamist extremist groups in conflict zones often escalate attacks during the holy month, in which Muslims typically fast during the day.

In the video, Baghdadi thanks God for the reestablishment of the Islamic caliphate, which he says had been “lost” for centuries.

“I do not promise you what the kings and rulers promise their subjects and followers — luxury and security and leisure,” he tells the men gathered before him. “But I promise what God promises those who believe in him.” Believers who obey God can expect an afterlife in heaven, he says.

“If you want security, respect God. If you want a livelihood, respect God. And if you want an honorable life, fight jihad in the name of God.”

Khalid Ali in Baghdad and Sharaf al-Hourani in Cairo contributed to this report.