Authorities in Bahrain say a bomb explosion has injured four policemen in the latest blast targeting security forces in the violence-wracked Gulf nation.

Anti-government factions have increased bombings as part of a 29-month uprising by Bahrain's Shiite majority seeking a greater political voice in the strategic Sunni-ruled kingdom, which is home to the U.S. Navy's 5th Fleet.

The Interior Ministry said Sunday's homemade bomb exploded in Janabiyah, a mostly Shiite area northwest of the capital Manama.

Last week, a policeman was killed and three injured in separate bombings. More than 60 people have died in Bahrain's unrest.

Some opposition groups are calling for major protests Aug. 14, inspired by the toppling of Egyptian President Mohammed Morsi. Bahrain's Interior Ministry warned it would take all measures to block such demonstrations.