A convoy of civilians was hijacked in southern Iraq Thursday and up to 14 people were abducted, the U.S. military said. Four Americans were believed to be among the captives, an official said.

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

An official familiar with the incident said preliminary reports being checked by the military indicated that the attack occurred at a checkpoint near Nasiriyah and that four Americans were believed to have been taken captive.

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The official, who requested anonymity because of the security situation in Iraq, said it appears that some of the convoy drivers had been released, and were being interviewed by the military. He said initial reports suggest that the attack occurred at a checkpoint in a location where normally there is no blockade.

The convoy was being operated by the Crescent Security Group. The company works mostly in Iraq, and its operations are based in Kuwait.

Whitman said he had no new details on the attack, adding that British forces were working with Iraqis to determine what happened. U.S. officials are also looking into the incident, according to the official.

Lt. Col. Christopher Garver, a U.S. military spokesman in Baghdad, confirmed that a convoy was attacked in the southern region of Iraq, but he also provided no other details.

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.