A British soldier was believed killed after armored vehicles came under attack in a possible "friendly fire" incident in southern Iraq, defense officials said Saturday. Four other soldiers were injured.

The Ministry of Defense said it was investigating reports the soldiers -- members of the Household Cavalry Regiment -- had been fired on by U.S. warplanes Friday.

"There is a suggestion this was a blue-on-blue incident," a spokeswoman said, using the military's term for accidental attacks on allied troops.

Britain's Press Association news agency, citing defense sources, said an American A-10 "tankbuster" plane targeted two British armored vehicles near Basra, where British troops have been battling forces loyal to Iraqi President Saddam Hussein.

British and American military officials at Central Command in Doha, Qatar, also said they were investigating the incident.

The A-10 is designed to fly low in support of ground troops, swooping in to knock out tanks and deflect artillery fire. In the 1991 Gulf War, a U.S. A-10 Thunderbolt -- predecessor of the current A-10 "Warthog" -- fired on a British armored convoy, killing nine servicemen.

Britain has 45,000 personnel, including 26,000 soldiers, involved in the U.S.-led war on Iraq.

Before Friday, four British servicemen were killed in "friendly fire" incidents since the conflict began. Four others have been killed in combat and 14 in accidents.