The announcement Saturday comes as security forces impose a virtual lockdown on the village of Eker, about 20 kilometers (12 miles) south of the capital Manama, where authorities say a homemade explosive exploded late Thursday. The policeman died the following day.
Security patrols set up checkpoints around the village and have tightly controlled movements.
More than 50 people have died in Bahrain's unrest since February 2011 when majority Shiites began an uprising for a greater political voice in the Sunni-ruled country.
Bahrain is home to the U.S. Navy's 5th Fleet.