BAGHDAD: The leader of the extremist group that has swept over much of northern Syria and Iraq on Tuesday called on Muslims to immigrate to the territory his group has seized to help build an Islamic state.

The 19-minute audiotape from Abu Bakr al-Baghdadi comes two days after his organization, the Islamic State of Iraq and the Levant, unilaterally declared the establishment of an Islamic state, or caliphate, in the land it controls. It also proclaimed al-Baghdadi the caliph, and demanded that all Muslims around the world pledge allegiance to him.

In his first remarks since that bold declaration, al-Baghdadi urged Muslims to come build their caliphate. He made a special appeal to those with practical skills — scholars, judges, doctors, engineers and people with military and administrative expertise — to come “answer the dire need of the Muslims for them.”

He also called on jihadi fighters to escalate fighting in the holy month of Ramzan, which began on Sunday. “In this virtuous month or in any other month, there is no deed better than jihad in the path of Allah, so take advantage of this opportunity and walk the path of you righteous predecessors,” he said. “So to arms, to arms, soldiers of the Islamics, fight, fight.”

The audio was posted on militant websites where the group has issued statements in the past, and the voice resembled that on other audiotapes said to be by the shadowy al-Baghdadi, an Iraqi militant who has rarely been photographed or appeared in public.

In a reflection of the havoc wreaked the past month by the Sunni insurgency led by the group, the United Nations said more than 2,400 people were killed in Iraq in June, making it the deadliest month in the country in years.

The Sunni insurgents’ advance, which has plunged Iraq into its worst crisis since the last US troops left in 2011, appears to have crested, at least for now, as it bumps up against majority Shiite areas, and as it seeks to consolidate its control of the territory already in hand. But in neighboring Syria, the group has continued to advance, seizing control of a border town on Tuesday.

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