"He was shot in the lower back from behind and seriously injured," a spokesman at Hiroshima Higashi Police Station said.

The victim was identified as Petty Officer third class Eric Heinz of Iwakuni Base, some 700 kilometres (435 miles) west of Tokyo.

He underwent surgery to remove the bullet at a Hiroshima hospital, the Japanese police official said, adding the wound was not life-threatening.

Iwakuni Base said Heinz was "shot at approximately 4:30 amSaturday) while walking down the street in the Hiroshima bar district."

"Heinz, a preventive medicine Corpsman here at the Branch Medical Clinic is currently listed in stable condition," the base said in an English-language statement.

"The Air Station Naval Criminal Investigative Service is coordinating with the Hiroshima Police that has responded and have jurisdiction in the conduct of this investigation," it said.

Heinz was with two fellow servicemen when he was shot, Japanese police said.

The lone attacker "suddenly fired one shot from the passenger-side window of the black sedan he was driving," the police officer said.

The attacker then got out of the car and pointed a gun at the two Marines who were trying to help the injured man. He did not fire but shouted something in Japanese and then drove away, police said.

Jiji Press news agency said the three servicemen were in civilian clothing at the time of the shooting.

The motive for the shooting is unclear.

Police are hunting the attacker who appeared to be aged between 25 and 35.

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