At least 51 people have died after a two of car bombs crashed through security checkpoints ringing the Iraqi holy city of Karbala.
Most of the victims were Shiite pilgrims travelling to observe yearly religious rituals.
It is the latest in a wave of attacks in recent days as insurgents test Iraqi security forces ahead of the planned US withdrawal at the end of the year.
There was no immediate claim of responsibility, but the bombings bore the hallmark of al Qaida and other Sunni-dominated extremist groups. They frequently target Shiite pilgrimages in the hope of re-igniting sectarian violence that brought Iraq to the brink of civil war just a few years ago.
Authorities estimate as many as 183 people were injured in the near-simultaneous blasts set off by suicide bombers driving cars packed with explosives.
Crowds of pilgrims headed to a Karbala hospital to donate blood for the wounded. Authorities said 11 soldiers and policemen were among the dead.
The series of attacks this week shattered a relative calm since the formation last month of a new government under Prime Minister Nouri al-Maliki, a Shiite whose family comes from the Karbala area.
The bombings were the latest in a three-day barrage of attacks across Iraq that have killed more than 120 people since Tuesday.
Earlier on Thursday, a suicide bomber rammed his explosive-packed car into the front gate of a police headquarters in the eastern Iraqi city of Baqouba, killing three.
Another, earlier strike on Shiite pilgrims walking to Karbala from Baghdad killed one and wounded 10.