Suicide 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 US 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-Qaida-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-Qaida in Iraq. However in the past, Iraqi officials have reported al-Baghdadi's arrest or killing, only to later say they were wrong. The US 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. Al-Baghdadi has been a key target for US 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. In Baghdad, a suicide bomber blew himself up among a group of Iraqis collecting humanitarian aid in a mainly Shi'ite 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 suicide bombings in Iraq, most recently during a Feb. 13 attack on Shi'ite 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.