No one was injured in the blast, which struck late yesterday in the mosque parking lot during evening prayers. But it was a rare explosion near the site of the royal residences, pointing to widening attacks by militant factions as part of the 29-month unrest.
Bahrain's majority Shiites are seeking a greater political voice in the strategic Sunni-ruled nation, home to the US Navy's 5th Fleet.
The recent rise in bombings suggests breakaway militant factions now operate outside the main Shiite political blocs.