Two bomb explosions kill at least 18 in Karachi ; motorcycles used in both attacks . 12 killed in the first explosion which targeted Shiite religious leaders on a bus . 12 killed in second attack which occurred outside a hospital treating victims of first blast . Attacks occurred during the Shiite observance of Arbaeen .
Two bomb blasts kill at least 18 in Karachi ; motorcycles used in both attacks . 12 killed in the first explosion which targeted Shiite religious observers on a bus . 6 killed in second attack which occurred outside a hospital treating victims of first blast . Attacks came during the Shiite observance of Arbaeen .