At least three persons were injured in the hand grenad attack and firing on three NATO trailers at Northern Bypass area of Karachi. The trailers were carrying vehicles for NATO forces in Kandahar, Afghanistan. According to police, Unidentified motorists attacked NATO trailers in Baldia Town area at Northern Bypass with hand grenades and opened firing. Three persons were injured in the firing. The injured were shifted to Civil Hospital. Police reached at the spot and started investigation.