U.S. troops captured 12 suspected militants Sunday in raids across Iraq, the military said.

The operations targeted members of Al Qaeda in Iraq and others suspected of building and planting roadside bombs, the military said in a statement.

Five suspects were detained in Ramadi, 70 miles west of Baghdad, the statement said. All were accused of involvement in car bomb and rocket attacks on U.S. troops, it said.

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Ramadi is the provincial capital of Iraq's volatile western Anbar province.

Also in Anbar, troops captured three suspects accused of ties with Al Qaeda in Iraq in Habbaniyah, 50 miles west of Baghdad, the military said.

In the capital, two men were detained for allegedly procuring bomb-making materials, the statement said.

And in Mosul, 225 miles northwest of Baghdad, two others were detained. They were accused of helping foreign fighters come to Iraq, as well as of involvement in roadside bomb operations, it said.

Meanwhile, a roadside bomb killed four U.S. soldiers patrolling western Baghdad, the military reported, while another soldier died in a non-combat related incident.

The roadside bomb killed the four soldiers Saturday, the military said in a statement. Small arms fire followed the blast, wounding another soldier.

The attack occurred as the soldiers were conducting patrols as part of a month-old security operation to end sectarian violence in the capital, the statement said.

So far this month, the soldiers' battalion had found eight weapons caches and two roadside bombs, as well as helping to rescue a kidnap victim, the military said.

Another soldier also died Saturday in a non-combat related incident, the military said in a second statement. The circumstances were under investigation, it said.

The victims' names were withheld pending family notification.

Two Iraqi policemen and two civilians were killed in separate incidents Sunday in Baghdad, police said.

A roadside bomb hit an Iraqi police convoy in eastern Baghdad, killing two policemen and wounding five others, authorities said. Two vehicles were damaged.

Later, police said a mortar round landed near a house in central Baghdad, killing a civilian and wounding another.

In Shorja market, Baghdad's most popular central shopping district, a man tossed a grenade into a group of workers, police said. One worker was killed and another was wounded. The suspect escaped through a nearby alley, they said.

The Shorja market has been bombed several times, including a large truck bomb last month. But the area was turned into a pedestrian zone after a U.S.-Iraqi security crackdown began in Baghdad on Feb. 14.

Also Sunday, an abandoned hotel exploded in an industrial area of Fallujah, 40 miles west of Baghdad. Police said insurgents had planted bombs in the three-story building and then detonated it at dawn. Half of the building was destroyed.

Iraqi troops had taken over part of the building's roof as a base, police said. There were no reports of casualties.

In Diwaniyah, 80 miles south of Baghdad, fierce fighting erupted between U.S. troops and elements of the Shiite Mahdi Army, police said. There were no reports of casualties, and the U.S. military had no immediate comment.

Police also found an unidentified man's body with signs of torture, dumped in central Diwaniyah.

Complete coverage is available in FOXNews.com's Iraq Center.