A bomb struck a crowd of mostly poor Shiites in Baghdad, killing at least 63 people and wounding more than 200 — including construction workers who were climbing onto a pickup truck that exploded after the driver offered them jobs.

The attack came as the U.S. military said four Marines had died in Anbar province on Monday.

In a press release from Camp Fallujah, the military said three Marines assigned to the 3rd Marine Aircraft Wing died from wounds sustained due to enemy action while a fourth Marine assigned to Regimental Combat Team 7 died from non-hostile causes. Their names were being withheld pending notification of next of kin.

Prime Minister Nouri al-Maliki, a Shiite who is under heavy political pressure for failing to curb the sectarian violence ransacking his country, condemned the attack in Baghdad and blamed it on Sunni extremists.

It was the second major attack in less than a month in which unemployed Shiites were lured to their deaths by a suicide bomber promising to hire them for the day. On Nov. 19, 22 people were killed and 44 were wounded when a minivan driven by a man promising work exploded in the mainly Shiite a southern city of Hillah.

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At least 54 other people were killed or found dead on Tuesday, including an AP Television News cameraman who was shot to death while covering clashes in Mosul. Aswan Ahmed Lutfallah, 35, was the third AP employee killed in the Iraq war since it started in March 2003. Five other people also were killed in the northern city.

In Baghdad, the bomber drove up to a group of day laborers and offered them jobs, then set off his explosives as they were climbing onto the pickup, Interior Ministry spokesman Brig. Abdul-Karim Khalaf said, adding that at least 63 people were killed and 236 were wounded.

Some police put the death toll as high as 71 and said earlier that it was a coordinated bomb attack involving a minivan and a car.

The blasts shattered storefront windows, dug craters in the road and set fire to several cars in the area.

Khalil Ibrahim, 41, who owns a shop in the area, suffered shrapnel wounds to his head and back.

"In the first explosion, I saw people falling over, some of them blown apart. When the other bomb went off seconds later, it slammed me into a wall of my store and I fainted," he said.

Residents rushed to the devastated area to see if friends or relatives had been killed or wounded. Mangled bodies were piled up at the side of the road and partially covered with paper. Two men sat on a nearby sidewalk, crying and covering their faces with their hands.

Another witness said the driver "lured the people to hire them as laborers, and after they gathered he detonated the vehicle."

Police Lt. Bilal Ali said most of the victims were Shiites from poor areas of the capital such as Sadr City.

Parliament speaker Mahmoud al-Mashhadani, a Sunni, also said the attack targeted poor people who were trying to feed their families, "turning them into pieces of flesh" and urged the deeply divided legislature of Shiites, Sunnis and Kurds "to find a solution" to Iraq's many problems.

Tayaran Square is located near several government ministries and a bridge that crosses the Tigris River to the heavily fortified Green Zone, where Iraq's parliament and the U.S. and British embassies are located.

Iraqis gather there daily to solicit jobs as construction workers, cleaners and painters. They buy breakfast at stands selling tea and egg sandwiches while they wait for potential employers to drive up, making them easy targets for suicide bombers.

The practice has become increasingly common amid high unemployment and soaring prices since the war started nearly four years ago, forcing men to hire themselves out daily to feed their families.

The Iraq Study Group report released earlier this month by a bipartisan commission in Washington said that unemployment ranges from 20 percent to 60 percent of Iraq's population.

Al-Maliki condemned the attack, calling it a "horrible crime."

"Iraq's security forces will chase the criminals and bring them to justice," he said.

The prime minister has been forced to defend his six-month-old government as he has come under fire from powerful politicians who accuse him of not doing enough to stop the sectarian violence that has spiraled since a Feb. 22 bombing that destroyed the golden dome of a revered Shiite mosque in Samarra.

Police, meanwhile, discovered a bomb hidden outside the mosque on Monday and it exploded while coalition bomb disposal officials were removing it, slightly damaging the building, the U.S. command said.

"This action by the terrorists shows they have no respect for Islam, and are only concerned about killing innocent civilians," said U.S. Lt. Col. Viet Luong.

Al-Maliki said Tuesday there was no alternative to his "national unity" government, arguing that talks between major partners in his ruling coalition to form a new bloc in parliament did not amount to a bid to unseat him.

Two key political figures, Vice president Tariq al-Hashemi, a Sunni Arab who was meeting with Bush Tuesday in Washington, and senior Shiite leader Abdul-Aziz al-Hakim, have been linked to behind-the-scenes efforts to form a new bloc in parliament that would replace the alliance now supporting al-Maliki's government.

"What is going on now is positive when the aim, contrary to what has been said, is to broaden the government's political base and not an attempt to undermine its ideology or to search for alternatives," al-Maliki told reporters in his first public comments on these efforts.

"There is no alternative in Iraq for this national unity government because it is the guarantee for the political process to continue," he said.

The White House has denied that any plans were afoot to dump al-Maliki, whose seven months in office have been defined by failure to curb growing violence and improve the lives of Iraqis.

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