A series of bombings rocked Baghdad on Tuesday, killing at least 15 people and wounding more than 100, and there were two separate attacks on U.S. military convoys in Baghdad in which at least three people were killed. The violence was the worst to hit the Iraqi capital since American combat troops withdrew on June 30, providing another test of Iraq's ability to defend itself as Prime Minister Nouri Kamal al-Maliki left for talks with President Barack Obama in Washington. Iraqi military and police officials have said they expected an increase in violence as armed groups aligned with political parties seek to gain influence before parliamentary elections scheduled for January. Otherwise, it was unclear who was behind the attacks, which struck disparate Sunni, Shiite and American targets and cropped up across the city and throughout the day. Bombs tore into a bustling sheep market, a crowd of impoverished job seekers and a funeral, security officials said. Three bombs went off in Sadr City, a predominantly Shiite neighborhood, and another in Dora, which is predominantly Sunni. At the sheep market, the dead included an 8-year-old girl and her year-old sister, whom the older girl was cradling in her arms, officials said. The first blasts went off at 5:30 a.m. in Sadr City, one of the poorest areas in the city. Two homemade bombs exploded seconds apart near a sidewalk where day laborers had gathered to wait for construction work, the police said. The bombs killed four people and wounded 31, mostly men but also several women who had been selling the men egg sandwiches, bowls of cream and tea for breakfast. 'We do not care about politicians or political issues,' Muhammad Ali, 32, a survivor, said later at a hospital where he was being treated for shrapnel wounds in his shoulder and back. 'Why do they attack us? The victims of this explosion are poor people who have been left to eat stones. Our bodies are already riddled with holes.' A few hours later, a third bomb exploded in Sadr City, this one at a crowded sheep market. Three people were killed -- the two sisters and their father -- as well as at least 20 sheep. In the southern Baghdad neighborhood of Dora, a car bomb blew up near a food market, killing two people and wounding six. In the northern Baghdad neighborhood of Baab al-Muadham, a bomb outside a mosque killed one person attending a funeral and wounded 13 others. And in the Karada neighborhood, 12 people were wounded in a roadside bombing apparently aimed at Abdul Latif Rasheed, the minister of water resources, officials said. He was unharmed. On Tuesday night, two bombs exploded at a popular market in the Husseiniya neighborhood, killing five people and wounding 24, the police said. And in the Rahmania area, a homemade explosive wounded five people, the police said. The attacks on the U.S. military came three weeks after combat troops had withdrawn from Baghdad and other cities, but the military is still allowed to move within the cities with permission from Iraqi security forces. In one attack, in the Shaab neighborhood about 8 a.m., the police said a homemade bomb exploded as a U.S. military patrol passed by. The U.S. military, however, said a car packed with explosives drove toward the convoy, but missed, striking pedestrians instead. Two civilians were wounded, the military said. Witnesses said at least one of the American military vehicles had been engulfed in flames. In the other attack, two men trying to throw grenades at a convoy in the Abu Ghraib district were shot to death by soldiers, the U.S. military said. Afterward, a firefight broke out between troops and people firing at them from an alley, the military said. One civilian was killed and four others were wounded in the brief battle. West of Baghdad, in Anbar province, a car bomb was detonated near a restaurant north of Ramadi, the provincial capital. Twenty people were wounded, the police said. The local police in Anbar said they suspected detainees released this week from U.S. prisons in Fallujah and Garma of carrying out the restaurant bombing. In a statement issued Monday when the U.S. military released the 39 prisoners, the military said it had 'followed a detailed release process to ensure the security of the people of Anbar and the safety of the detainees.' In the restive northern city of Mosul, gunmen shot and killed a policeman on Tuesday, a day after five police officers in the city were fatally shot, the Iraqi police said. 