At least 49 people have been killed in an attack on a group of Shia worshippers in the southern Iraqi city of Karbala.
An Iraqi police officer and a witness said that Monday's bombing was carried out by a female suicide bomber.
A US statement said the identity of the bomber remained unknown.
But Brigadier-General Raed Shakir Jawdat, Karbala's police chief, who said 43 people were killed and another 73 wounded, claimed what took place was a bomb explosion, not a suicide blast.
Iranians killed
Salim Kadhim, a spokesman of the Karbala health directorate, said on Tuesday that the dead included seven Iranian pilgrims.
Another eight Iranians were wounded.
The Karbala blast was the deadliest in a series of attacks that left scores of Iraqis dead, including six youths killed when mortar rounds hit a soccer field in eastern Baghdad.
Two US soldiers also were killed on Monday in a roadside bombing north of Baghdad, bringing the American death toll closer to 4,000.
The US embassy and military subsequently issued a joint statement blaming al-Qaeda in Iraq for the Karbala attack.
The bomber struck after the worshippers had gathered at a sacred historical site about 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.
Police later closed the area around the twin golden dome mosques and blocked all roads leading to the sites.
Karim Khazim, the city's chief health official, said seven of those killed were Iranian pilgrims who had travelled to the holy site.