BAGHDAD - Iraqi security officials said they captured one of the most wanted leaders of the al Qaeda-linked Sunni insurgency Thursday, an arrest that could deliver a significant blow to an intensified campaign of attacks. Two separate suicide bombings killed at least 54 people.

The officials identified the arrested man as Abu Omar al-Baghdadi who leads the Islamic State of Iraq, an umbrella group of Sunni militant factions that is believed dominated by al Qaeda in Iraq. However in the past, Iraqi officials have reported al-Baghdadi's arrest or killing, only to later say they were wrong. 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 Qaeda fighters.

In Washington, Pentagon spokesman Bryan Whitman said the U.S. military was working to verify who was captured.

"I can't confirm ... the capture of a senior al Qaeda member or that it was Baghdadi," he said. But he said he had no reason to doubt the credibility of the report.

"I certainly hope that it's true," he said, adding that his capture "would be very good news."

Al-Baghdadi has been a key target for U.S. and Iraqi forces for years. But little is known about his origins or real influence over insurgent groups. Those groups have staged a series of high-profile attacks in recent weeks, apparently including the two suicide blasts Thursday in Baghdad and north of the capital in Diyala province.

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 he was captured.

In 2007, Iraq's government reported that al-Baghdadi had been killed and released photos of what it said was his body. Later, security officials said they had arrested al-Baghdadi. In both cases, the U.S. military said at the time it could not be confirmed and the reports turned out not to be true.

In March, a 17-minute audio message attributed to al-Baghdadi called Washington's announcement of a troop withdrawal timetable from Iraq "recognition of defeat." The statement was carried on militant Web sites.

Thursday's attacks were 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.

American soldiers who specialize in clearing bombs from roads boarded a plane Thursday from Iraq to the Taliban heartland in southern Afghanistan, part of the largest movement of personnel and equipment between the two war fronts.

In the Baghdad bombing, a suicide bomber blew himself up among a group of Iraqis collecting humanitarian aid in a mainly Shiite area, killing at least 22 people, the military said.

The attacker struck as police were distributing Iraqi Red Crescent food parcels in the central neighbourhood of Karradah, the main Baghdad military spokesman said.

It not immediately clear who carried out the attack, but one witness said it appeared to be a woman. Women have been used in suicide bombings in Iraq, most recently during a Feb. 13 attack on Shiite pilgrims in Musayyib.

Muhanad Harbi, the owner of a motorcycle parts shop near the blast site, said he saw a woman wearing a black robe wade into the crowd waiting for aid packages. He said it appeared she detonated an explosives belt.

Shanoon Humoud, 70, sat weeping amid burned food packages scattered on the ground. Her husband, her son and two grandchildren were killed in the blast.

Humoud said she was in her apartment praying when she heard the blast.

"I came down to look for my relatives who getting the food," she said. "But I couldn't find them."

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.

Some police were among the 22 people killed and 35 people were wounded, the military said.

North of Baghdad, a suicide bomber killed at least 32 people in a crowded restaurants, said Sadir Jaafar, the deputy head of the Diyala provincial council. He said 60 were wounded.

The U.S. military gave a lower toll, saying at least 20 were killed. But conflicting casualty tolls are common.

Military spokesman Derrick Cheng said initial reports showed about 45 people were also wounded when the suicide bomber detonated an explosives vest in Muqdadiyah, an insurgent hotbed about 90 kilometres northeast of Baghdad.

The Pentagon's top Middle East adviser, Deputy Assistant Defense Secretary Colin Kahl, said Wednesday that insurgent attacks in Iraq will probably increase as U.S. forces start to leave, but there's no plan now to delay troop departures.

U.S. President Barack Obama is deploying 17,000 more troops to Afghanistan to beef up U.S. operations there.

The 4th Engineer Battalion began sending troops and equipment -- everything from giant tow trucks and bulldozers to desks and chairs -- last week.

U.S. military commanders have said the sharp decline in violence in Iraq and the increasing capabilities of Iraq's security forces made it possible to transition the soldiers.