BAGHDAD — Three Iraqi soldiers threw themselves on a suicide attacker wearing an explosives vest at an Army Day celebration Sunday — an act of heroism America said likely prevented many more deaths. Iraqi police said at least 11 people were killed in the blast, the deadliest in a series of bombings in Baghdad.

One of the attacks in the capital killed an American soldier — one of two American deaths announced yesterday.

Shortly before the bomber struck the Army Day festivities, about two dozen Iraqi soldiers were standing outside the offices of a local nongovernmental agency pushing for unity in Iraq. The troops, their AK–47 rifles raised in the air, chanted pro-army slogans and a common anti-insurgent taunt: “Where are the terrorists today?”

An Associated Press photographer, Hadi Mizban, was about five yards away from the suicide attacker when he blew himself up on a narrow street in the central Karradah area.

“The blast happened as civilians were giving flowers to soldiers and sticking them in the muzzles of their guns,” Mr. Mizban, an Iraqi national, recalled. “It was a jubilant scene.”

Afterward, he said, the street was littered with bodies, weapons, and shoes. Dazed soldiers and policemen carried their bloodied colleagues to nearby pickup trucks that whisked them to a hospital. “There was a severed head on the street and some of the soldiers that I was photographing earlier were dead. Those who survived panicked, pulling back from the scene and shooting in the air,” the 40-year-old Mr. Mizban said.

Among the dead were four police officers, three Iraqi soldiers, and four civilians, a police officer said on condition of anonymity because he was not authorized to speak to reporters. At least 17 people were injured.

An American military statement said five people were killed. The discrepancy could not immediately be explained.

These martyrs gave their lives so that others might live,” an American military spokesman, Lieutenant Colonel Steve Stover, said.

In the north in the Iraqi city of Mosul, meanwhile, three apparently coordinated explosions targeted two Christian churches and a convent, local officials, and the American military said. Four people were wounded.

“They are cowards,” a priest told the Associated Press, refusing to give his name because he feared for his safety. “This act will only foster our insistence to remain loving brethren to all sects in the city. I’m sure that those who committed this crime are far away from religion.”

The attacks in Mosul began midafternoon when a parked car bomb exploded near a Chaldean Catholic Church, causing damage but wounding no one. About 30 minutes later, another car bomb exploded in the eastern part of the city near an Assyrian Christian Church, damaging the building and wounding four passersby.

Nearly simultaneously, a bomb planted near a Chaldean convent in western Mosul exploded, damaging the structure and a few nearby houses. No one was hurt.