BAGHDAD - Hundreds of Iraqi and U.S. troops cordoned off sections of Baghdad's Sadr City slum Wednesday and conducted raids in an apparent effort to find five British citizens whom Iraqi officials believed were abducted by the Shiite Mahdi Army militia.

British Embassy officials held ongoing talks with Iraqi officials about the situation, Britain's Foreign Office said. Britain's COBRA crisis committee was also to meet for the second day.

The five men were pulled out of a Finance Ministry office by about 40 heavily armed men in police uniforms in broad daylight Tuesday and driven in a convoy of 19 four-wheel-drive vehicles toward Sadr City, according to Iraqi officials in the Interior and Finance ministries.

A top Interior Ministry official, who refused to be identified because he was not authorized to speak to the media, said the authorities were working on the assumption the five were abducted by the Mahdi Army of radical cleric Muqtada al-Sadr because the area they were taken from is controlled by the militia.

British Foreign Secretary Margaret Beckett said officials were doing all they could to ensure the men were released quickly.

"This is clearly a very distressing time for all concerned," she said upon arriving at a Group of Eight meeting in Potsdam, Germany.

"It is not helpful at this stage to speculate on what might have happened," she said. "We are working closely with the Iraqi authorities to establish the facts and doing all we can to secure their swift and safe return."

Soon after the abduction, Iraqi forces established a special battalion of soldiers and police officers to search for the men, said Brig. Gen. Qassim al Musawi, an Iraqi army spokesman.

"We are conducting search operations near the site where the abduction took place," he said. "Maybe today or in the coming few days, we will find them with the help of secret intelligence."

Residents of Sadr City said hundreds of U.S. and Iraqi troops sealed off areas of the Shiite neighborhood overnight and carried out a series of arrest raids that lasted until dawn. The residents spoke on condition of anonymity because they feared reprisals for talking to the Western media.

The U.S. military said it had arrested five suspected militants and one suspected leader of a militant cell during early morning raids in Sadr City. Those arrested were believed part of a cell that smuggled weapons from Iran and sent militants to Iran for training, the statement said.

The statement did not link the raid to the missing men.

Two civilians were killed and four others injured in crossfire from gunbattles that broke out in one of the raids, police said. The civilians had been sleeping on their roofs in a traditional Iraqi custom to escape the brutal heat, police said, speaking on condition of anonymity because they were not authorized to talk to the media.

The U.S. military, responding to a query from The Associated Press, said it had conducted two raids in Sadr City but that no shots were fired.

A roadside bomb that apparently targeted a passing police patrol in Sadr City, missed and killed one civilian and wounded four others, police said.

Hours after the abduction, Joe Gavaghan, a spokesman for Montreal-based security firm GardaWorld, confirmed that four of its security workers and one client were kidnapped. All four GardaWorld workers are British citizens, he said, declining to provide more details.

A spokesman for BearingPoint, a McLean, Va.-based management consulting firm, said one of the company's employees, apparently the client referred to by Gavaghan, was among those abducted.

If the work of the Mahdi Army, the kidnappings could be retaliation for the killing by British forces last week of the militia's commander in Basra.

Canon Andrew White, the Anglican vicar of Baghdad who lives in the Garda World compound and is involved in efforts to free the men, said it's "a possibility" the kidnapping was a response to the killing.

"We're working very hard with various religious leaders to try to work at this issue, but its not easy. It's very, very difficult," he told AP, about efforts to free the men.

White said he had only carried out indirect talks with possible mediators and refused to comment on who may have taken the men. "We haven't spoken directly to anybody," he said, adding that no demands had been issued by the captors.

"It's a very complex situation at the moment, and we have to be very careful," he said.

The raid was reminiscent of an attack by the Shiite militiamen, dressed as Interior Ministry commandos, who stormed a Higher Education Ministry office Nov. 14 and seized as many as 200 people. Dozens of those victims have never been found.

Maj. Gen. Abdul-Karim Khalaf, the Interior Ministry spokesman, said Tuesday's abduction was carried out by men wearing police uniforms who showed up at the Finance Ministry data collection facility in 19 four-wheel drive vehicles of the type used by police. He said the band of kidnappers sped off across the Army Canal to the east. Sadr City, the Shiite Mahdi Army stronghold, is directly east of the canal.

"We are pursuing this case very vigorously, first to release them, secondly to establish the truth of what happened, who was responsible," Foreign Minister Hoshyar Zebari told BBC radio.

Zebari said that the government has long believed that its security forces were infiltrated by militia members.

"The number of people who were involved in the operation -- to seal off the building, to set roadblocks, to get into the building with such confidence -- (means they) must have some connection," he said.

In other violence, several mortar rounds apparently targeting a U.S. military base in Fallujah missed their mark and landed instead on a courthouse and in a residential neighborhood, killing nine civilians and wounding 15, according to police and Dr. Anas al-Rawi of Fallujah General Hospital.

A police convoy was struck by a roadside bomb in the town of Hamzah, south of Baghdad, killing two guards and injuring two others, a police officer said, speaking on condition of anonymity because he feared reprisals for talking to the media.

Gunmen in three cars ambushed three soldiers who had stopped to drink orange juice in Karbala, 50 miles south of Baghdad, and stole the nearly $396,000 in salaries they were transporting to their unit, an army official said, speaking on condition of anonymity for fear of reprisals.

The three soldiers were arrested on suspicion of involvement in the theft, the official said.

On Tuesday, the U.S. military said 10 American soldiers were killed in roadside bombings and a helicopter crash the day before, making May -- with at least 113 fatalities -- the third-deadliest month of the war for U.S. troops.

The Islamic state of Iraq, an al Qaeda front group, claimed responsibility for shooting down the helicopter in a statement posted on a militant website. The claim could not be independently verified. The military did not say if the helicopter was shot down or had mechanical problems.