It was not known whether the five were still in the area or whether the gunmen were involved in the kidnapping, said Capt. Tane Dunlop, a spokesman for British forces. He said two of the gunmen were killed.

Nine other civilians were in the convoy when it was attacked Thursday near Basra. The men were Asian and have been released, said the contractors' employer, Crescent Security Group.

"We have four American security contractors and one Austrian unaccounted for," he said in a telephone interview from the firm's headquarters in Kuwait. "All the civilian truck drivers have been accounted for, a mix of men from countries such as India, Pakistan, the Philippines."

The Iraqi official, who declined to be named for personal reasons, refused to say how many vehicles were in the convoy, who hijacked it and how the freed captives were released, explaining that he didn't want to jeopardise the work of US and British forces.

A US Embassy official, who refused to be identified because he was not authorized to release the information, said the convoy included 43 heavy trucks and six security vehicles. Some of the hijackers were dressed as Iraqi police and those men took away 20 vehicles, he said.

Dunlop said in a telephone interview from Basra that the hijacking occurred Thursday at 1 pm in Safwan, an Iraqi city near the Kuwait border. He said the convoy was coming from Kuwait.

At dawn Friday, British ground forces and helicopters searched an area of Safwan for gunmen who had attacked coalition forces in the past few days when about 10 of them opened fire from farm buildings, Dunlop said. The British and US forces returned fire, killing two of the gunmen, Dunlop said.

An Iraqi police officer confirmed the fighting and gave higher casualty figures, saying five of the gunmen and one British soldier also had been wounded. But Dunlop could not immediately confirm that. The Iraqi officer spoke on condition of anonymity because he is not authorised to talk to the media.

The officer said the Crescent Security Group convoy had been stopped at a checkpoint on Thursday by Iraqi men, some of them wearing police uniforms.

The Crescent Security Group company works mostly in Iraq, and its operations are based in Kuwait. Many of its managers and employees are American.

In Washington, Pentagon spokesman Bryan Whitman said Thursday that preliminary reports suggested the attacked convoy included about 19 vehicles.

A State Department official informed the family of Paul Reuben, 39, a former Minneapolis police officer who was working as a security contractor in Iraq, that he was among those captured, his brother, Patrick Reuben, told the Star Tribune newspaper and KSTP-TV in St. Paul, Minnesota.

Italy formally handed over security responsibility of the southern Dhi Qar Province to Iraqi forces in late September, and British troops handed over control of the adjacent southern Muthana province in July.

Meanwhile, insurgents killed one US soldier in Iraq's restive province of Diyala in a small arms fire attack, the military said Friday.

The soldier was killed Thursday, raising to 11 the number of American military deaths in three days.

The latest fatality raise the military's losses in Iraq since the March 2003 invasion to 2,859, according to an AFP count based on Pentagon figures.