A hand grenade was tossed off Sunday at a unit of security forces at a major intersection in west Beirut , police said. The grenade was tossed off a bridge by assailants on a motorbike at the Barbir intersection, near Mazraa section of Beirut and fell near a checkpoint for security forces in this Sunni Muslim neighborhood of the Lebanese capital. Three from the unit of the security forces were injured according to police reports.Beirut area and nearby suburbs have seen three explosions in the last week, killing a woman and injuring nearly 30 people. One in Ashrafiyieh, a Christian area, one in Verdun, a predominantly Moslem Sunni area and one in Aley, a Druze resort town east of Beirut . The violence came as Lebanese troops were fighting Islamic militants at the Palestinian refugee camp of Nahr el-Bared in northern Lebanon. Scores of people have been killed in the northern fighting.