But little is known about his origins or real influence over insurgent groups, which have staged a series of high-profile attacks in recent weeks, including, apparently, the two suicide blasts Thursday in Baghdad and north of the capital in Diyala province.
The U.S. military has even said al-Baghdadi could be a fictitious character used to give an Iraqi face to an organization dominated by foreign al-Qaida fighters.
But Iraqi security forces said he was in custody.
Iraqi state television quoted military spokesman Maj. Gen. Qassim al-Moussawi as saying al-Baghdadi was arrested in Baghdad. Security officials also told The Associated Press that he was captured. The officials spoke on condition of anonymity because they were not allowed to release the information.
No other details were immediately available about the arrest. In the past, Iraqi officials have announced arrests of key militant figures that later proved wrong.
In March, a 17-minute audio message attributed to al-Baghdadi called Washington's announcement of a combat withdrawal timetable from Iraq "recognition of defeat." The statement was carried on militant Web sites.
Although violence is down sharply around Iraq compared with recent years, high-profile attacks blamed on insurgents have been on the rise recently.
In Baghdad, a suicide bomber blew himself up among a group of Iraqis collecting humanitarian aid in a mainly Shiite area in Baghdad, killing at least 22 people, the Iraqi military said.
The attack was the latest in a series of high-profile bombings that have raised concern of an uptick in violence as the U.S. military scales back its forces before a planned withdrawal by the end of 2011.
The bombing occurred just after noon as Iraqi police were distributing aid parcels near Tahariyat Square in the central neighborhood of Karradah, according to the office of the main Baghdad military spokesman.
Abbas Ibrahim, a 24-year-old college student, described pools of blood on the ground and the smell of burned flesh in the air.
"We regret that violence has come back to Baghdad," he said. Issam Salim, 35, was wounded by shrapnel as he was waiting for a bus about 30 yards from the explosion.
"I turned around as I fell to the ground and saw a big fire break out with black smoke," he said from his hospital bed. "Women and children are crying from pain beside me in the hospital. Some of them suffered burns."
Some police were among the 22 people killed and 35 other people were wounded, according the military.
North of Baghdad, the U.S. military said a suicide bomber killed at least 20 in a crowded restaurant.
Military spokesman Derrick Cheng said initial reports showed about 45 people were also wounded when the suicide bomber detonated an explosives vest Thursday in Muqdadiyah, northeast of Baghdad. Muqdadiyah is an insurgent hotbed about 60 miles (90 kilometers) northeast of Baghdad.
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