Four bombs rock Baghdad

The violence in Baghdad seems to be at the same level as it was before the U.S.-led surge pacified the city. Four separate explosions thundered here on Wednesday - including a suicide attack in the Shiite militia stronghold of Sadr City –at least 53 people are killed.

Meanwhile, U.S. troops killed five suspects and captured 30 others in a raid in Iraq's western Anbar province, a day after police uncovered 17 decomposing corpses beneath two school yards in the provincial capital.

The U.S. military also announced a discovery made nearly a week earlier _ 3,000 gallons of nitric acid hidden in a warehouse in downtown Baghdad. U.S. forces found the acid - a key component in fertilizer but also explosives - during a routine search operation last Thursday, the military said.

Iraqi troops took charge of security Wednesday in the southern province of Maysan, a region that borders Iran and the fourth province to come under full Iraqi security control since the 2003 U.S. invasion.

Violence continued to rage Wednesday, with mortar attacks and bombings across the country.

In the deadliest of the Baghdad attacks, a suicide car bomber crashed into an Iraqi checkpoint at an entrance to Sadr City, killing at least 30 and wounding 45 in the capital's largest Shiite Muslim slum, police said. The east Baghdad enclave is home to some 2.5 million people.

The bomber exploded in a traffic jam of several civilian cars at the checkpoint. Five Iraqi security officers were among the dead, police said.

A huge plume of black smoke rose from a jumble of at least eight incinerated vehicles. Bystanders scrambled over twisted metal to drag victims from the smoldering wreckage, as Iraqi troops staggered around stunned.

Earlier, a parked car exploded near a private hospital in the central neighborhood of Karradah - killing 11 people and wounding 13, police said. The blast damaged the Abdul-Majid hospital and other nearby buildings.

Another parked car bomb detonated in Sadriyah market in central Baghdad, killing eight people and injuring 26 - all civilians, police and hospital officials said. About five civilian cars were burned. The market was last hit by a car bomb in February, which killed 137 people.

The fourth explosion was from a bomb left on a minibus in the northwestern Risafi area, killing four people and wounding six others, police said.

Also in Baghdad, four policemen were killed Wednesday afternoon when gunmen ambushed their patrol south of the city center, police said. Six pedestrians were also wounded in the attack.

U.S. officials have cited a slight decrease in sectarian killings in Baghdad since a U.S.-Iraqi security plan was launched on Feb. 14. But the past week has seen several spectacular attacks on the capital, including a suicide bombing inside the parliament building and a powerful attack that completely collapsed a landmark bridge across the Tigris river.

"We've seen both inspiring progress and too much evidence that we still face many grave challenges," Maj. Gen. William Caldwell, a U.S. military spokesman, told reporters Wednesday in Baghdad. "We've always said securing Baghdad would not be easy."

A ceremony was held in Maysan's provincial capital of Amarah, 320 kilometers (200 miles) southeast of Baghdad, and was attended by senior Iraqi and coalition officials including Iraqi National Security Adviser Mowaffak al-Rubaie and the British commander in southern Iraq, Maj. Gen. Jonathan Shaw.

At the handover ceremony, al-Rubaie said in order for a timetable to be set for the withdrawal of foreign troops, Iraqi forces and local authorities have to be ready to take over. He was apparently referring to calls by some Sunni groups and followers of radical Shiite cleric Muqtada al-Sadr to set a timetable for such a pullout.

"We should work to create these circumstances in all provinces,in order to revert security to Iraqis and end the foreign presence," said al-Rubaie, who represented Prime Minister Nouri al-Maliki, the commander-in-chief of Iraq's armed forces.

Al-Maliki was supposed to attend the ceremony but his trip was canceled without explanation.

In other violence Wednesday, two brothers were killed and a policeman was hurt in a gunbattle in downtown Baqouba, 60 kilometers (35 miles) northeast of Baghdad, police said. The dead were believed to be civilians, caught in the crossfire as police fought unidentified gunmen.

Farther north, 32 mortar shells rained down on Iraqi army checkpoints in two neighborhoods of Mosul, 360 kilometers (225 miles) northwest of the capital, police said. Six soldiers, a policeman and a pedestrian were injured.

An Iraqi army officer and two soldiers were also wounded at dawn in Tal Afar, 75 kilometers (47 miles) west of Mosul, when gunmen attacked their checkpoint as well, police said.

In the ethnically-mixed city of Kirkuk, 290 kilometers (180 miles) north of Baghdad, an investigative judge at the city's criminal court was injured in a drive-by shooting, police said.

Judge Ayad Ali Asaad, a Turkoman, was driving with his wife and a guard when gunmen blocked their way and opened fire, police said. All three were wounded.

Mortar shells also hit several neighborhoods south of Baghdad's center early Wednesday, wounding at least four civilians in two separate attacks, police said. Two bodies of men handcuffed and killed execution-style turned up Wednesday in Dora, also in southern Baghdad.

The night before, a civilian was killed and four injured when a mortar round hit their house in western Baghdad, police said. Also Tuesday, a roadside bomb went off next to an ambulance in Samarra, 95 kilometers (60 miles) north of Baghdad. Four people, including a patient in the back of the vehicle, were wounded, police said.

The U.S. raid took place early Wednesday near Karmah, a town northeast of Fallujah, which lies 65 kilometers (40 miles) west of Baghdad.

American forces raided a group of buildings suspected of being used by militants, and found explosives inside one of them, the military said in a statement. A helicopter was called in, and dropped precision-guided bombs on the cluster of buildings, it said.

Meanwhile, troops came under fire and reacted in "self-defense," the statement said _ killing five Iraqis and wounding four others.

The wounded were taken to a military hospital and remained in U.S. custody. Twenty-six others were captured as well, the military said.

Later, the military issued another statement that one suspect was killed and eight captured in two more raids Wednesday north of Baghdad. Some of the suspects were believed to be linked to al-Qaida in Iraq, and to a militant cell that has used chlorine in car bombings, the statement said.

The bodies found a day earlier at school yards in Ramadi, Anbar's provincial capital, were discovered after students and teachers returned to the schools a week ago and noticed an increasingly putrid odor and stray dogs digging in the area, Police Maj. Laith al-Dulaimi said.

He said one body had not yet been recovered from a separate burial site behind one of the schools because authorities feared it was booby-trapped with a bomb.

Ramadi had been a stronghold of Sunni insurgents and al-Qaida fighters until recently, when the U.S. forces in the region and the Iraqi government successfully negotiated with many local tribal leaders to split them off from the more militant insurgent groups.

Thousands of young Sunni men have joined the police force in Anbar province and have taken up the fight against the Islamic State of Iraq, the umbrella organization that includes al-Qaida.