At least 170 people have died in a series of co-ordinated attacks on Shia worshippers in Baghdad and Kerbala. A further 41 were killed attacks on Shias in Pakistan.
The US military said three suicide bombers killed 58 people in Baghdad at the Kadhimiya mosque, and Ahmed al-Safi, a leading cleric in Kerbala, said at least 112 people had been killed in Kerbala, a Shia holy city 68 miles south of Baghdad.
More than 400 people were wounded in the two cities.
The near-simultaneous attacks devastated an annual ritual - banned under the Sunni Saddam - during which Shias honour a revered figure killed in battle 1,324 years ago.
In Kerbala, where two million worshippers had gathered, rescuers raced through the streets with bodies laden two or three high onto wooden vegetable carts, searching for a doctor or an ambulance.
Enraged Shias turned on Iranian pilgrims after the blasts - even though an Iranian Interior Ministry official said 40 to 50 Iranians were among the dead and wounded in the attacks on the two cities.
As yet, no one has claimed responsibility for the attacks. Leaders of Iraq 's 60 per cent Shia majority accused the attackers of trying to ignite civil war.
Several members of Iraq 's US-appointed Governing Council blamed the attacks on Abu Musab Zarqawi, a Jordanian whom Washington suspects of working for al-Qaeda inside Iraq .
In a separate attack in Baghdad, guerrillas threw a bomb at a US military vehicle, killing one American soldier and seriously wounding another, the army said.
The death takes to 379 the number of US soldiers killed in action since the start of the US-led war in Iraq nearly a year ago.
Shias were also targeted today in southwestern Pakistan where at least 37 people were killed and more than 150 wounded on Tuesday in an attack by suspected Sunni Muslim radicals, hospital sources said.
Angry Shias threw stones at US troops they claimed had failed to protect them.