Two policemen opened fire on U.S. troops visiting an Iraqi police station in the northern city of Mosul on Tuesday, killing an interpreter and wounding four American soldiers, 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 confirmed that one interpreter was killed and four U.S. soldiers and another interpreter were wounded by small-arms fire as they were meeting at an Iraqi police station about 2 p.m. in Mosul, about 225 miles northwest of Baghdad.

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

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

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

Al-Jubouri said an Iraqi police captain who was commanding the regiment also was wounded.

The attack comes just over two weeks after a suicide car bomber struck a U.S. patrol in Mosul, killing four American soldiers and an Iraqi interpreter in the deadliest single attack against U.S. forces in nine months.

With violence unrelenting in Mosul, U.S. and Iraqi forces launched a new military offensive dubbed Operation New Hope aimed at rooting out al-Qaida and other Sunni insurgents in the city and the surrounding Ninevah province.

Several previous operations have failed to quell the violence in the volatile area, where insurgents remain active and ethnic tensions between Kurds and mainly Sunni Arabs have been on the rise.

On Nov. 25, two U.S. troops — a Marine and a soldier on a transition team working with the Iraqis — were killed when a gunman in an Iraqi army uniform opened fire while they were distributing aid southwest of Mosul.

An Iraqi soldier also ambushed U.S. soldiers in a courtyard of an Iraqi military base in a dangerous Sunni Arab neighborhood in Mosul on Nov. 12, killing two Americans and wounding six before he died in the subsequent gunbattle.

And in December 2007, an Iraqi soldier also allegedly shot and killed a U.S. captain and a sergeant during a joint operation in Mosul.