An Iraqi health official says the death toll in Monday's bombing in Karbala has risen to 52.
The blast coincided with a visit by US Vice-President Cheney in Iraq
The bomb exploded near the shrine of Imam Hussein, a pilgrimage centre for Shia Muslims.
Most reports identified a female suicide bomber as the perpetrator, but the Karbala police chief said it had been a bomb planted in a crowded area.
The attack overshadowed a trip to Iraq by US Vice-President Dick Cheney to discuss security across the country.
About 75 people were injured in the blast.
It was the deadliest of a number of violent incidents in which at least 78 Iraqis died.
Officials suspect al-Qaeda insurgents were behind the bombing in the city, 80km (50 miles) south of Baghdad, but no group has claimed responsibility.
Six youths were killed in Baghdad when mortars hit their sports field.
Two US soldiers were also killed in a roadside bombing north of Baghdad.
Mr Cheney was holding talks with Kurdish leaders in northern Iraq on the last day of his visit.
Earlier on Tuesday, he met American soldiers stationed at a military base in Balad, north of Baghdad, where he had stayed the night.
He rallied the troops, telling them they were there to bring freedom to a region where it was being suppressed.
"As President Bush has said, the war on terror is an ideological struggle and as long as this part of the world remains a place where freedom does not flourish, it will remain a place of stagnation, resentment and violence ready for export," he said at the outdoor rally.
His tour coincides with the fifth anniversary of the US-led invasion of Iraq, launched on 20 March, 2003.
He will move on to Oman, Saudi Arabia, Israel, the occupied West Bank and Turkey.