Another nine civilians who were traveling with the convoy when it was attacked Thursday near the city of Basra have been released, said an official for Crescent Security Group.

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

The official refused to say how many vehicles were in the convoy, who hijacked it and how the freed captives were released, saying he didn't want to jeopardize U.S. and British efforts. He declined to be named for personal reasons.

"I'm not sure what the British and U.S. military have put in motion, and I don't want to release too much information in case it compromises whatever they may be doing. But we're working very closely with them to get this resolved," the official said.

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

In Basra, Capt. Tane Dunlop, a spokesman for British forces, said the hijacking occurred Thursday at 1 p.m. in Safwan, an Iraqi city near the Kuwait border, and that four Americans and an Austrian were still being held.

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

An official familiar with the hijacking said Thursday that initial reports suggested that the attack occurred at a checkpoint in a location where normally there is no blockade.

NBC television reported that the kidnappers were wearing uniforms.

The State Department 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, Minn.

Britain's Ministry of Defense said Friday that no British civilians or military forces were attacked or taken hostage during the hijacking.

In Baghdad, a spokeswoman for the U.S. military would only confirm on Friday that "an incident occurred at a checkpoint." She added that officials would probably provide more information later.

Italy formally handed over responsibility for security in 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.