The US-appointed Iraqi Governing Council (IGC) declared three days of mourning after Tuesday’s carnage, which threatened to be the worst since the fall of Iraqi leader Saddam Hussein 11 months ago, and urged the war-torn country's people to remain calm, patient and united.
Two of Iraq's top Shia clerics blamed the attacks on the United States for failing to seal the country's borders from foreign fighters.
"We put the responsibility of ensuring security in the country
and of protecting sacred Shia sites on the occupational forces because they have left our borders open to infiltrators," said Grand Ayat Allah Bashir Najafi from the the city of Najaf, 160km south of Baghdad.
For his part, Abd al-Aziz al-Hakim, a member of Iraq's interim Governing Council and head of the Supreme Council of the Islamic Republic (SCIRI), a Shia party, said: "The occupying forces are incapable of protecting the Iraqis and they don't let the Iraqis protect themselves."
Earlier at a press conference Shia, Sunni and Kurdish members of the IGC accused Abu Mussab al-Zarqawi, a Jordanian-born Palestinian suspected of ties to al-Qaida.
In the city of Karbala, at least one assailant detonated explosives as mortars were fired at an estimated two million Shia, including many Iranians, leaving 112 people dead.
Dozens of others were injured in five coordinated blasts, according to Aljazeera’s correspondent.
Scenes of carnage
"Ambulances, and even civilian cars, were transferring casualties to hospitals," our correspondent reported.
Shia cut themselves as they beg
for al-Husayn's forgiveness
Also on Tuesday, at least 70 people were killed when four blasts rocked the holiest Shia mosque in the north of Baghdad.
US military officials said three assailants also detonated explosives simultaneously. Iraqi police said a fourth potential attacker was detained.
Witnesses said an explosion was caused by a rocket fired at the crowd at al-Kadhimiya mosque. But other witnesses said they saw attackers detonating explosives at the mosque entrances and inside the building.
The attacks were carried out on Ashura, the holiest day of the Shia calendar, when Shia mourn the slaying of al-Husayn, grandson of the Prophet Muhammad, more than 1300 years ago.
A spokesman for Polish occupation forces, meanwhile, said two suspects were caught red-handed as they prepared to launch mortar attacks in Karbala.
AFP's correspondent saw crowds kicking a man senseless, punching him and throwing rocks at him, while shots were fired in the air. A television cameraman was almost lynched by the crowd who thought he was involved in the attacks.
Of the victims in Baghdad and Karbala, about 40 to 50 were Iranian pilgrims, said Iranian interior ministry spokesman Jahanbakhsh Khanjani in Tehran.
And in Najaf, three attacks were foiled in the past 24 hours, said a member of Iraq's Governing Council.
Al-Hakim said his group's militia had thwarted the attacks.
They also confiscated rocket-propelled grenades and mortars from cars in Karbala, he said.
Constitution signing delayed
After the explosions, members of the IGC said they would delay signing an interim constitution, which they hammered out on Monday. The ceremony may take place on Friday.
The temporary constitution, which is aimed to see Iraq through a transitional period into next year, is due to be signed on Wednesday.
Under the law, Iraq will become a decentralised state with two official languages where Islam will be a source of legislation, but not the basis for it.
The international community was swift in condemning the series of explosions. The Arab League "forcefully" slammed the deadly blasts as "terrorising innocent civilians".
Doctors were barely able to deal
with the scores dead, wounded
"These are barbarous acts which did not take into account the holy character of Ashura," it said in a statement.
Arab League Secretary General Amr Musa urged Iraqis to stay united "in order not to leave open the chance for those who want to tear apart Iraqi unity."
A prominent Saudi Sunni cleric also condemned the blasts, warning that they were aimed at fuelling sectarian strife among Muslims.
"There might be infiltrators attacking the Shia to make it appear they are being targeted by Sunnis and the other way round. It is in the interest of both (Iraqi) Sunnis and Shia to agree on putting out this fire and not to react to such provocations," said Shaikh Salman al-Udah.