Homicide bombers struck a humanitarian aid distribution point and a crowded restaurant in separate attacks Thursday in Iraq, killing at least 78 people in the deadliest day of violence to strike the country this year.

The bombings are the latest in a series of high-profile attacks that have raised concern of an uptick in violence as the U.S. military scales back its forces in Iraq ahead of a planned withdrawal by the end of 2011.

The latest attacks came as Iraqi security officials said they captured one of the most wanted leaders of the Al Qaeda-linked Sunni insurgency, an arrest that could deliver a significant blow to an intensified campaign of attacks.

The officials identified the arrested man as Abu Omar al-Baghdadi who's believed to lead 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.

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 homicide blasts Thursday in Baghdad and north of the capital in Diyala province.

In Baghdad, a homicide bomber blew himself up among a group of Iraqis collecting humanitarian aid in a mainly Shiite area, killing at least 31 people, the Iraqi military said.

The attacker struck as police were distributing Iraqi Red Crescent food parcels in the central neighborhood 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 homicide bombings in Iraq, most recently during a Feb. 13 attack on Shiite pilgrims in Musayyib.

Muhanad Harbi, a shop owner near the blast site, said he saw a woman wearing a black robe wade into the crowd. 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 were getting the food," she said. "But I couldn't find them."

Some police were among the 31 people killed and 51 people were wounded, the military said.

North of Baghdad, a homicide bomber killed 47 people, including Iranian pilgrims, in a crowded restaurant, said Iraqi and U.S. military officials.

Military spokesman Derrick Cheng said 47 people were killed and about 69 were wounded when the homicide bomber detonated an explosives vest near Muqdadiyah, an insurgent hotbed about 60 miles northeast of Baghdad.

Iraqi police and hospital officials said another 65 were wounded. Most of the wounded were pilgrims, the officials said.

The officials spoke on condition of anonymity because they were not authorized to release the information.

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.

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.

Also Thursday, 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.

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

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.