Two US soldiers also were killed Monday in a roadside bombing north of Baghdad, bringing the American death toll closer to 4,000 as the US-led war enters its sixth year. At least 3,990 members of the US military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

The violence marred overlapping trips by Vice President Dick Cheney and Sen. John McCain to Baghdad. Their visits were aimed at touting recent security gains and stressing Washington's long-term commitment to fighting insurgents in Iraq.

The American Embassy and the military issued a joint statement condemning the "barbaric attack" and blaming it on al-Qaida in Iraq.

The Karbala attack came after the worshippers had gathered at a sacred historical site about a kilometer (half a mile) from the golden domed shrine of Imam Hussein, a grandson of the Prophet Muhammad who was killed in a seventh-century battle.

A police officer, speaking on condition of anonymity because he wasn't authorized to release the information, said the attacker was a woman – as did a witness.

The US military described the attack as a suicide operation but put the casualty toll at 40 Iraqis killed and 65 wounded. The US statement said the identity of the bomber remained unknown.

Brig. Gen. Raed Shakir Jawdat, Karbala's police chief, said 43 people were killed and 73 wounded. He denied it was a suicide attack, saying a bomb had been planted in the area. The discrepancies could not immediately be resolved.

Karim Khazim, the city's chief health official, said seven of those killed were Iranian pilgrims who had traveled to the holy site.

AP Television News footage showed a man carefully picking up pieces of flesh and wires apparently from a fuse as evening prayer services were broadcast from loudspeakers nearby.