A homemade bomb exploded in a Shi’ite Muslim village in Bahrain on Tuesday, wounding two policemen, the interior ministry said, nine days after another blast in the Gulf Arab kingdom killed three security men.

Bahrain has been grappling with unrest by majority Shi’ites over the past three years demanding political reform and an end to perceived discrimination in the Sunni Muslim-ruled country. Bahrain denies any discrimination against Shi’ites.

Bomb attacks have increased since last year, raising concern about further instability in the Western-allied kingdom where the U.S. Fifth Fleet is based as a bulwark against Shi’ite giant Iran across the Gulf.