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Homicide attackers unleashed car bombings against police buildings in Iraq's biggest Shiite (search) city Wednesday morning, striking rush-hour crowds and killing at least 68 people, including 16 children incinerated in their school buses.

The attacks wounded about 200 people and marked a revival of devastating homicide bombings, which had not been seen during this month's battles between U.S. forces and homegrown guerrillas across Iraq.

Basra Gov. Wael Abdul-Latif (search), a member of the Iraqi Governing Council, blamed Al Qaeda (search), but a U.S. counterterrorism official said it was premature to make such judgments.

In Fallujah, the bloodiest battlefield in April, an agreement aimed at bringing peace to the city ran into trouble Wednesday. Insurgents attacked Marines, prompting fighting that killed 20 guerrillas. Marines said most weapons turned in by residents were unusable, undermining a crucial attempt at disarming fighters.

About 350 miles to the south, in Basra (search), bombers struck at 7 a.m., just as the city's main street market, near one of the targeted police stations, was opening for the day. Shoppers were headed to the stalls of vegetables and other goods, and children were passing on their way to school.

The attackers detonated four cars packed with missiles and TNT in front of three police stations -- one of them next to Basra's main street market -- and a police academy. An hour later another car bomb went off outside the police academy in Zubair, a largely Sunni town about nine miles from mainly Shiite Basra.

Police discovered two other car bombs before they were detonated and arrested three men in the vehicles, Abdul-Latif said.

The blast in front of the Saudia police station wrecked and charred vehicles, including school buses taking kindergartners and girls ages 10-15 to school.

Dead children, burned beyond recognition, were pulled from the wreckage. One body, black as carbon but apparently an adult, was taken away in a pickup truck.

An Associated Press reporter counted the bodies of 10 kindergartners and six older girls at Basra's Teaching Hospital, where the morgue was full and corpses were left in the halls.

Nine of the dead and 36 of the wounded were police, Abdul-Latif said.

President Bush condemned the homicide attacks in Basra and in the Saudi capital, Riyadh, where a car bomb blasted national police headquarters, killing at least four people and wounding 148.

The U.S. counterterrorism official, speaking on the condition of anonymity, said at this point there is no evidence to suggest the bombings in Iraq and Saudi Arabia are related.

Bush said it was imperative that the United States stay the course in Iraq and help establish a democracy there.

"The Iraqi people are looking at Americans and saying, 'Are we going to cut and run again?"' Bush told more than 1,500 AP-member newspapers at the cooperative's annual meeting. "And we're not going to cut and run if I'm in the Oval Office."

The last major homicide attack in Iraq also targeted Shiites: Homicide bombers detonated explosives bodies among thousands of pilgrims at shrines in Karbala and Baghdad on March 2. At least 181 people were killed.

U.S. officials said they believed those attacks were planned by Abu Musab al-Zarqaqi, a Jordanian linked to Al Qaeda who they say intends a campaign of attacks to spark a civil war between Iraq's Shiite Muslim majority and Sunni minority.

But since the start of April, attention has shifted to Iraqi insurgents, with U.S. troops besieging the Sunni stronghold of Fallujah and a radical Shiite militia launching a revolt in the south. Those two fronts -- plus a flare-up of insurgent violence around Baghdad and across the country -- have stretched U.S. forces in Iraq.

Maj. Gen. Martin Dempsey, commander of the Army's 1st Armored Division, suggested the bombings were timed to coincide with the relative quiet over the past few days.

"If I were them (the attackers), I think I would probably want to stay in the news. And the way you stay in the news is space (attacks) out, you conduct attacks sequentially, not simultaneously" with other violence, he told AP.

Throughout the month, U.S. coalition officials have warned that sudden terror attacks remained a threat, and security was increased during Shiite religious ceremonies in Karbala on April 11.

The U.S. counterterrorism official said those behind Wednesday's attack may include Sunni extremists attacking a Shiite area, a tribal group, former regime elements or the network belonging to al-Zarqawi.

"It is just premature to draw any conclusions," the official said.

U.S. officials and military commanders say foreign Islamic militants are among the fighters they seek to uproot from Fallujah -- and they have suggested al-Zarqawi could be in the city.

But the relationship between Iraqi insurgents and foreign militants remains unclear. While Washington contends Iraq is a center of the war on terror, U.S. forces have captured few foreigners among hundreds of Iraqi insurgents. Al-Zarqawi complained of poor cooperation with Sunni guerrillas in a letter to Al Qaeda leaders that the U.S. military said it intercepted in January.

Wednesday's was the bloodiest attack in Basra, a city in Iraq's far south that has seen little insurgent violence. Of the roughly 200 wounded, 168 were in critical condition.

The blast outside the Saudia station heavily damaged its facade and left a crater six feet deep and nine feet wide. When British troops in charge of Basra showed up to help, angry Iraqis blocked their way, saying they failed to secure the city.

Iraqi Interior Minister Samir Shaker Mahmoud al-Sumeidi said the Basra attack resembled the March 2 homicide bombings and Feb. 1 bombings in Irbil that killed 109 people.

"Today, we all have lost children who are part of Iraq's future which the terrorists want to destroy. The Iraqi government ... confirms its resolution on defeating this cancer which is called resistance," al-Sumeidi said.

U.N. envoy Lakhdar Brahimi also condemned the attacks, saying "I don't think that killing kids can be justified or explained."

Four British soldiers were wounded in the police academy blasts, two of them seriously, the British Ministry of Defense said.

In Fallujah, the four-hour battle cast a shadow over an agreement reached by negotiators aimed at bringing peace to the city 35 miles west of Baghdad.

The fighting began with an ambush by 13 insurgents on Marines, who called in Cobra gunships that killed 10 of the attackers, Marine Lt. Col. Brennan Byrne said. Nearly three dozen insurgents then joined a running battle with Marines that ended with warplanes dropped two 500-pound bombs. Ten more insurgents were killed, Byrne said.

"I think that is being thought of as a major breach," Byrne said of the battle.

The U.S. military has warned that major fighting could resume if the agreement fails. City leaders negotiated the deal with U.S. officials, but the Americans say much hinges on whether the guerrillas comply.

As a result of the failure to disarm, Marines halted the return of families to Fallujah. Commanders did not say how many weapons were turned in.

North of Baghdad, a U.S. soldier died and two others were injured in a vehicle accident unrelated to fighting, the military announced Wednesday. No names were released.