BAGHDAD - US troops killed five suspects and captured 30 others Wednesday 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.

Iraqi schoolchildren inspect holes where buried bodies were found, in their school yard in Ramadi, 115 kilometers (70 miles) west of Baghdad, Iraq, Tuesday, April 17, 2007. [AP]

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

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

Two brothers were killed and a policeman was hurt in a gunbattle in downtown Baqouba, 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, 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, 50 miles west of Mosul, when gunmen attacked their checkpoint as well, police said.

In the ethnically-mixed city of Kirkuk, 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, 60 miles north of Baghdad. Four people, including a patient in the back of the vehicle, were wounded, police said.

The US raid took place early Wednesday near Karmah, a town northeast of Fallujah, which lies 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 US custody. Twenty-six others were captured as well, the military 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 US 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.