Four U.S. soldiers were wounded and their interpreter was killed at a police station in northern Iraq on Tuesday, in an attack that Iraqi security sources said was carried out by rogue Iraqi police.

The sources said that two members of a police force tasked with guarding bridges opened fire at the American soldiers and their interpreters during a visit to the police station in Mosul, Iraq's most violent city,.

Lieutenant Colonel David Doherty, a U.S. military spokesman, said four U.S. soldiers and one interpreter were injured, and another interpreter was killed. He did not immediately confirm the identity of the attackers.

One security source, who declined to be identified, said the attackers had fled. While violence in Iraq has dropped sharply from its peak in 2006 and 2007, Mosul and the surrounding Nineveh province, seen by the U.S. military as the last holdout of al Qaeda and other Sunni Islamist groups, remain bloody.

Two U.S. soldiers were shot dead by an Iraqi soldier in Mosul in November.

At least nine U.S. soldiers were killed by hostile fire in Iraq in February, nearly six years after the U.S.-led invasion to oust Saddam Hussein. The four U.S. combat deaths registered in January were the lowest monthly toll since the war began.