A hand grenade was thrown late Sunday at a unit of security forces at a major Beirut intersection, injuring two policemen, an army soldier and two civilians, police said. The grenade was tossed off a bridge by assailants at the Barbir intersection and fell near a checkpoint for security forces in the Sunni Muslim neighborhood, a major commercial artery in the Lebanese capital. The assailants fled and police were in pursuit. Two policemen, an army soldier stationed there and two civilians who happened to be passing by the area were slightly injured, the police said. At least one vehicle was damaged, according to police, speaking on customary condition of anonymity.