U.S. forces fired an artillery barrage in southern Baghdad Sunday morning, rocking the capital with loud explosions. The death toll from a homicide car bomb attack in the Shiite holy city of Karbala rose to 68 as residents dug through the debris of heavily damaged shops.
The blasts in Baghdad came a day after the U.S. military announced the deaths of nine American troops, including four killed in separate roadside bombings south of Baghdad and five in fighting in Anbar province, a Sunni insurgent stronghold west of the capital.
American troops also detained 72 suspected insurgents and seized nitric acid and other bomb-making materials during raids on Sunday targeting Al Qaeda in Iraq in Anbar province, a Sunni insurgent stronghold west of the capital, and Salahuddin province, a volatile Sunni area northwest of the capital, the U.S. military said.
The size and the pattern of the explosions, which began after 9 a.m. and lasted for at least 15 minutes, suggested they were directed at Sunni militant neighborhoods along the city's southern rim. Such blasts have been heard in the evenings but are rare at that time of day.
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In a brief statement to The Associated Press, the U.S. military said it fired the artillery from a forward operating base near Iraq's Rasheed military base southeast of Baghdad, but provided no other details.
Iraqis in the southern region of the city said American and Iraqi forces had stepped up their operations in the Dora area of southern Baghdad starting Saturday night.
Authorities in northern Iraq imposed an indefinite curfew in the Sunni stronghold of Samarra after leaflets signed by rival insurgent groups threatened policemen if they did not quit their jobs and promised to target any oil company that wants to explore in the area. The warnings to the policemen were signed by Al Qaeda in Iraq and threatened to destroy their houses if they didn't comply.
Leaflets signed by a separate insurgent umbrella group calling itself the Mujahedeen of Samarra warned against oil exploration in the area and were posted on the walls of mosques in central Samarra, 60 miles north of Baghdad.
Samarra also was one of the targets of the raids announced by the U.S. military, which said 36 suspected insurgents with alleged ties to Al Qaeda in Iraq who were taken into custody there.
In the Anbar province city of Karmah, 50 miles west of Baghdad, American forces found 20 five- gallon drums of nitric acid and other bomb-making materials, the statement said.
Iran, meanwhile, agreed to attend a U.S.-backed regional conference on Iraq set for this week in Egypt — a major break as Iraq seeks support from its neighbors in quelling its sectarian violence and getting back on its feet economically. Tehran said Foreign Minister Manouchehr Mottaki will lead the delegation to the May 3-4 meetings.
Arab countries also are expected to demand that al-Maliki's government do more to reach out to disgruntled Sunni Arabs before they pledge substantial aid to the country.
Separately, an Iraqi Sunni lawmaker urged his party to withdraw from the Shiite-led government if it fails to better protect citizens from sectarian bloodshed.
Khalaf al-Ilyan, one of the three leaders of the Iraqi Accordance Front, said at a news conference in Amman, Jordan, that his party should set a timetable for the government to end mass killings and "stop threatening lawmakers" from his party.
The Accordance Front holds five Cabinet posts and 44 seats in the 275-seat Iraqi parliament.
The blast in Karbala, 50 miles south of Baghdad, took place about 7 p.m. Saturday in a crowded commercial area about 200 yards from the shrines of Imam Abbas and Imam Hussein, major Shiite saints. The shrines, some of the country's most sacred, were not damaged, police said.
Police first thought the explosion was caused by a parked car bomb, but Ghalib al-Daami, a Karbala provincial council member, said Sunday it was a homicide car bomber in the busy commercial center.
Residents on Sunday gathered around the large crater left in the road by the bomb, and pools of water left by firefighters fighting the blaze were still tinged red with blood.
Salim Kazim, the spokesman for Karbala health directorate, said the casualty figures had risen to 68 dead after some of the wounded died and more bodies were found on the roofs of buildings or in the rubble, and 178 were wounded.
As police maintained a vehicle ban in the city, people began digging through the rubble of damaged shops, lifting debris from the powerful explosion, which had shot flames into the air.
"The explosion was so powerful that it threw me up into the air," said Haidar Ismail, one of the many patients lying in overcrowded rooms at Imam Hussein Hospital with bandages covering their wounds and burns.
Saturday's attack was the second car bomb to strike the city's central area in two weeks. On April 14, 47 people were killed and 224 were wounded in a car bombing in the same area.
Ghalib al-Daami, a provincial council member who oversees security matters, noted how close the homicide bomber came to the Imam Abbas shrine, which with the others draws thousands of Shiite pilgrims from Iran and other countries. That suggested the attack was aimed at killing as many Shiite worshippers as possible.
In other developments Sunday:
— Two roadside bombs exploded in separate areas of a predominantly Shiite area in southeastern Baghdad, killing three civilians and wounding nine, police said.
—Gunmen seriously wounded Amal al-Moudares, one of Iraq's best known radio and television journalists, in an attack near her home in Baghdad, police said.
— The Islamic State of Iraq, an umbrella group of Sunni militants that includes Al Qaeda in Iraq, claimed responsibility for a suicide truck bombing Friday in the western city of Hit, saying it was targeting the police chief. The attack killed nine Iraqi security forces and six civilians, although police chief Hamid Ibrahim al-Numrawi and his family were unharmed.
— In a statement posted on a militant Web site, Al Qaeda in Iraq claimed responsibility for a homicide car bomb Thursday that killed 10 Iraqi soldiers at a checkpoint in Khalis, a longtime flashpoint city 50 miles northeast of Baghdad. Ten soldiers and five civilians were wounded, police said.
— An employee at a communications center in the northern city of Mosul was killed in a drive-by shooting, police said.
— Police found the bullet-riddled body of an unidentified man in southwestern Baghdad.
— A sniper shot to death an Iraqi woman near a market in western Baghdad, police said.
Complete coverage is available in FOXNews.com's Iraq Center.