CAIRO (AP) -- The first online statement from the new leader of al-Qaida's affiliate in Iraq claims that the militant network is returning to strongholds from which it was driven by U.S. forces and their Sunni allies before the American withdrawal at the end of last year.

The al-Qaida leader claimed the militant group is preparing operations to free prisoners and assassinate court officials.

The audio identified the speaker as Abu Bakr al-Baghdadi, who became head of the Islamic State of Iraq in 2010. It was posted late Saturday on a website regularly used by the militant movement to make statements.

Al-Baghdadi warned the United States that it would soon suffer militant attacks on its territory.

He also invited Muslims to come to Iraq to join his militants.

The statement comes as Sunni insurgents, now believed to be dominated by the ISI, step up attacks against Shiites, government officials and other targets, in what is seen as a bit to undercut the authority of Iraq's government and revive sectarian conflict.

"I bring you good news: We are starting a new phase in our struggle with a plan we named `Breaking the walls,' and we remind you of your priority to free the Muslim prisoners," he said.

"At the top of your priorities regarding targets is to chase and liquidate the judges, the investigators and the guards," he said.

He urged tribal leaders to send their men to join al-Qaida as it returns to areas from which it withdrew - a reference to reverses the ISI suffered at the hands of U.S. forces and allied Sunni militias in 2007 and 2008.

"I urge you to send your sons to join the ranks of the mujahideen (fighters) in defense of your religion and honor," he said. "The majority of the Sunnis in Iraq support al-Qaida and are waiting for its return."

Al-Baghdadi devoted almost half of the 33-minute speech to the uprising against the regime of Syrian President Bashar Assad, member of a Shiite offshoot sect. The rebels are largely Sunnis, and fighters from al-Qaida, including Iraqis, are believed to have taken an increasingly active role in recent months.

"Our people there have fired the coup de grace at the terror that grasped the nation (Syria) for decades ... and taught the world lessons of courage and jihad and proved that injustice could only be removed by force," he said.

He warned the Syrian rebels "not to accept any rule or constitution but God's rule and Shariah (Islamic law). Otherwise, you will lose your blessed revolution."

Al-Baghdadi became the leader of the group after Abu Omar al-Baghdadi, who was not related, was killed together with the other top al-Qaida leader in Iraq, Egyptian Abu Ayyub al-Masri, in an air and ground assault by a team of U.S. and Iraqi forces on April 18, 2010.