Two policemen opened fire on U.S. troops visiting an Iraqi police station in the northern city of Mosul on Tuesday, killing a U.S. soldier and an Iraqi interpreter and wounding three other Americans, officials said.

It was the fourth such shooting in the Mosul area in just over a year purportedly involving Iraqi security forces, underscoring concerns about infiltration in a city considered the last urban stronghold of Sunni insurgents.

The U.S. military said one interpreter was killed and that a U.S. soldier died later of his wounds after the troops came under small-arms fire at a police station.

It said three other Americans also were wounded in the 2 p.m. attack in Mosul, about 225 miles northwest of Baghdad.

The military provided no other details, saying the attack was still under investigation.

Police spokesman Brig. Gen. Saeed Ahmed al-Jubouri said two Iraqi police officers began shooting at the Americans as they were visiting a police unit that protects bridges.

He said the attackers fled the area in a car and that a manhunt was under way.