By Ross Colvin

BAGHDAD (Reuters) - The U.S. military said on Monday it had killed 60 militants during a week-long offensive in northern Iraq against al Qaeda which has proved a resilient foe and has resisted previous attempts to drive it from the region.

The offensive in four northern provinces and Baghdad's southern suburbs was launched on January 8 by the U.S. military, which regards al Qaeda as the single greatest threat to Iraq's security and has blamed it for an upsurge in suicide bombings.

In Baghdad, gunmen killed appeals court judge Amir Jawdat al-Naeib as he drove to work on Monday. Naeib's driver was also killed. Militants have frequently targeted judges, academics, other professionals and their families.

The new offensive is seen as part of the U.S. strategy of reducing violence to give Prime Minister Nuri al-Maliki's government time to cement the security gains with political progress towards national reconciliation.

The military said in a statement that U.S. and Iraqi forces had killed 60 militants, detained 193 and found 79 weapons caches containing thousands of rounds of ammunition, explosives and home-made bombs during the offensive in northern Iraq.

Troops had found one cache in an underground bunker complex with several rooms during operations in Diyala, a volatile, religiously mixed province north of Baghdad.

But the fighting has not been one-sided. Police said seven policemen were killed when the house they were searching blew up in the town of Buhriz just south of Baquba, Diyala's capital.