Deadly attacks rock Baghdad, Karbala
An Iraqi boy grieves after multiple explosions in Baghdad on Tuesday.
CNN's Brent Sadler on a series of powerful explosions that rocked Karbala.
Angry Iraqis throw stones at U.S. troops in the aftermath of explosions at a Baghdad mosque.
CNN's Jane Arraf describes the scene after explosions ripped through an Ashura celebration in Baghdad.
BAGHDAD, Iraq (CNN) -- Suspected insurgents killed scores of people Tuesday in well-organized, simultaneous attacks in Baghdad and the holy city of Karbala on the holiest Shiite Muslim day of the year, U.S.-led coalition officials said.
Iraqi authorities swiftly blamed Abu Musab al-Zarqawi, a Jordanian who is suspected of calling for attacks on Shiites to promote the fight against the U.S.-led coalition.
It was the deadliest day in Iraq since President Bush declared an end to major combat operations on May 1, 2003.
At least 100 people were killed in Karbala with about 300 wounded, a doctor at a hospital told CNN.
Earlier, Brig. Gen. Mark Kimmitt, a U.S. Army spokesman, said 85 people were killed and 230 were wounded in Karbala.
The death toll in Baghdad was at least 58 people, Kimmitt said, and 200 others were wounded.
Three suicide bombers detonated explosives around the al-Kadamiya mosque in Baghdad, and a fourth was apprehended before his device exploded, Kimmitt said.
One suicide bomber was discovered in Karbala, he said, and explosives were found alongside a road outside the city, along with mortar rounds. Six people were apprehended in Karbala, which is 55 miles (88 kilometers) south-southwest of the capital, he said.
Ahmed al-Haelali, a judge in Karbala in charge of investigating the explosions, said he believes nine suicide bombers were responsible for the strikes in his city.
He showed CNN small ball bearings, nails and springs retrieved from the bombing sites. The judge said these materials indicated to him that suicide bombers were responsible.
The attacks came as thousands of worshippers jammed the streets to attend festivals marking Ashura, the most important holy day on the Shiite Muslim calendar.
The U.S.-appointed Iraqi Governing Council, which condemned the attacks, declared a three-day mourning period. As a result, the signing of an interim Iraqi constition that had been set for Wednesday will be delayed, said Abdul Aziz al-Hakim, a member of the council.
Governing Council member Adnan Pachachi accused "terrorist and evildoers" of "trying to destabilize the country through sectarian strife."
In Washington, White House spokesman Scott McClellan condemned "these brutal terrorist attacks in strongest terms" and speculated that the perpetrators were "remnants of the former regime and foreign terrorists" who "are enemies of freedom."
Paul Bremer, the top U.S. civilian administrator in Iraq, said the attacks were committed "to provoke sectarian violence among Muslims."
The devastating strikes come weeks after the coalition found a letter apparently written by Zarqawi to al Qaeda in Afghanistan calling for strikes against Shiites to keep the insurgency alive and taking credit for other attacks.
The Governing Council members cited the letter as a lead in the search for the origins of Tuesday's attacks. The coalition has posted a $10 million bounty for Zarqawi.
"One of the chief suspects in this would be Zarqawi" because the techniques and methods were similar to those of other terror attacks, Kimmitt said.
U.S. criticized on security
An injured Shiite pilgrim is taken to a hospital after expolsions at a shrine in Baghdad.
The attacks in Baghdad and Karbala took place about 10 a.m. (2 a.m. ET).
Shiites from Iraq -- as well as pilgrims from the largely Shiite nation of Iran and other Shiite communities -- traveled to both cities to mark the day, the 10th day of the month of Muharram. It is the period when Ali's son al-Hussein, grandson of the prophet Muhammad, died in battle centuries ago. (Full story)
In the Ashura ceremony, Shiites flog their bodies to identify with the suffering of the martyr Hussein. Shiites were heavily persecuted under Saddam Hussein's regime, and Saddam banned certain religious practices on the holy day.
Shiite institutions have not been immune from attack since Saddam, a Sunni, was deposed last year. In August, a car bomb attack killed scores of people at a Shiite shrine in Najaf.
In Karbala, video showed dozens of bodies -- many dismembered and burned beyond recognition -- and many others wounded.
Police said they believe five suicide bombers may have slipped through a tight security cordon before the end of the Ashura festivals, and a series of up to nine explosions were heard about two miles (3 kilometers) from the city center.
Police broke up an angry demonstration after the blasts blaming the United States for the carnage.
Polish soldiers from the coalition surround Karbala but were not inside the city, where Iraqi police are responsible for order. Even after the violence, pilgrims continued their religious observances.
In Baghdad, police said pilgrims had filled the streets of a neighborhood for the religious ceremony when the attacks took place.
At least one explosion detonated in al-Kadamiya mosque, killing a number of people -- including women and children -- the mosque's imam said.
Grenade fragments were found in the mosque's courtyard, and authorities said there is a strong indication improvised explosive devices and grenades were behind that blast. Initially, authorities said they thought rockets hit the mosque. (Full story)
The mosque's imam blamed foreigners, saying Iraqis would never conduct such attacks.
He criticized the U.S. military for not providing adequate security, but the Army disputed that assertion. Angry pilgrims began throwing stones at Iraqi police and U.S. soldiers.
In London, British Prime Minister Tony Blair said the attacks signify there is no "clearer struggle between good and evil."
Jordan's King Abdullah II, appearing with Blair, slammed the "heinous" attacks "targeting innocent Shia" for the purpose of dividing and conquering.
In Pakistan, meanwhile, a gunmen opened fire on Shiite worshippers in Quetta, killing at least 38 people and injuring others, medical and police officials said. (Full story)
• In a separate attack Tuesday in Baghdad, a U.S. soldier was killed and another seriously wounded when an improvised explosive device was thrown at their military vehicle, U.S. military sources said.
• The explosions in Baghdad and Karbala came a day after the Iraqi Governing Council agreed on an interim constitution. The constitution is intended to govern the nation until an elected assembly can draft and make into law a permanent charter.
CNN's Jane Arraf and Brent Sadler contributed to this report.