March 2 (Bloomberg) -- Bombers attacked Shiite Muslims in Iraq and Pakistan on a holy day, killing at least 184 people and wounding about 590 in a challenge to security in both countries. U.S. officials said a man they have described as an al-Qaeda associate, Abu Musab al-Zarqawi, may be behind the Iraqi attacks.

Iraqis marking the observance of Ashura were targeted in almost simultaneous attacks in the Iraqi capital Baghdad and the venerated Shiite city of Karbala about 60 miles south. At least 58 people were killed and 200 wounded at a Baghdad mosque and 85 people were killed and 230 wounded in and near Karbala, U.S. Army Brigadier General Mark Kimmitt said in Baghdad.

``This was a clear and tragically well-organized act of terrorism,'' Dan Senor, a spokesman for the U.S.-led coalition in Iraq, said in Baghdad as he answered questions alongside Kimmitt.

At least 41 Shiites were killed and more than 160 wounded in a bomb blast and gun assault on a procession in the city of Quetta, Pakistan, according to tallies from two hospitals. City officials imposed a curfew as the assailants were sought. There was no immediate evidence the attack, which police said involved shooting by possibly three gunmen following by explosions, was coordinated with the Iraqi bombings.

The Iraq attacks created the largest single-day death toll since the fall of Saddam Hussein's regime in April and came as the U.S. works toward the transfer of sovereignty to an Iraqi body by June 30. The U.S.-picked Iraqi Governing Council wrapped up an interim Iraqi constitution yesterday.

Basra Bombs Thwarted

Police in the U.K.-patrolled southern city of Basra took into custody four individuals suspected of readying bombs there, including two women wearing belts with explosives in a Shiite procession, the Associated Press reported. Two men were arrested in connection with a car found to contain a bomb.

U.S. soldiers responding to the mosque in Baghdad were shouted at and stoned by irate Iraqis, a reaction that Kimmitt described as ``absolutely understandable'' in a moment of acute grief. Senor said Iraqis who watched American forces defeat Hussein's regime in three weeks last year are trying to grasp why the same army can't stop the resistance assaults.

The bombings were the most deadly in Iraq since two suicide bombers struck Kurdish political offices in the northern city of Arbil on Feb. 1, killing at least 100 people. A mosque in the holy city of Najaf was bombed in August, killing leading cleric Ayatollah Mohamad Baqir Al Hakim along with more than 80 other people.

Bombs, Mortars

At least three suicide bombers attacked the Al-Kadhimiya mosque in Baghdad, while a fourth person, wearing an explosives- filled vest, was captured, Kimmitt said. In Karbala, one suicide bomber targeted the city center, explosives were remotely detonated alongside a road outside the city and mortars were fired, Kimmitt said. Six people are being held and questioned by the Iraqi police in connection with the attacks.

Kimmitt said the 38-year-old Zarqawi is a ``chief suspect'' in the Iraq attacks. The U.S. military last month made public a letter it said was written by Zarqawi that described a plan to provoke a war within four months between Iraq's Sunni Muslims and the majority Shiites.

Adel Abdel-Mehdi, a Governing Council member, said he and other council members believed Zarqawi was responsible.

Zarqawi is suspected ``just by the methods that have been used in the past, just by the techniques that have been used in the past; by the axiom of suicidal, spectacular, symbolic,'' assaults, Kimmitt said. ``All those would point to some sort of transnational organization.''

Blair on Zarqawi

In London, U.K. Prime Minister Tony Blair and visiting Jordanian King Abdullah II both implicated Zarqawi in the attacks. Blair said a small, active group inside Iraq is trying to set Shiite against Sunni to foment unrest.

Jack Straw, the foreign secretary of the U.K., which has the second-largest military commitment inside Iraq, said earlier that he thought the attacks were timed to send a message against Iraqi unity.

``It is no coincidence in my judgment that these events have occurred both on days of celebration for the Shiite community and of devotion by them, but also just a day after there was the very good news from Iraq of the agreement for what amounts to an interim constitution,'' the minister said.

Landmark Observance

Hundreds of thousands of Iraqis turned out to observe Ashura, the first celebration permitted since the mostly Sunni Baath Party of Saddam Hussein took power almost three decades ago. Ashura marks the death in battle almost 1,300 years ago of Imam Hussein, a grandson of the Prophet Mohammed.

In Beirut, a spokesman for Iraq's leading Shiite cleric, Grand Ayatollah Ali Sistani, blamed American soldiers for the attacks, saying they were responsible for the security. Sheikh Hamed Khafaf said U.S. officials had ignored repeated requests to bolster security for the pilgrims.

Kimmitt said the U.S. left security operations inside mosques and directly around them to Iraqi police officers, though U.S. soldiers do set up ``outer cordons'' and conduct searches.

To contact the reporter on this story: Todd Zeranski in New York at tzeranski@bloomberg.net

Last Updated: March 2, 2004 13:09 EST