Security forces in the Pakistani city of Karachi have been ordered to shoot-at-sight to stem violence in which 80 people have been killed so far.In the recent wave of violence, which is widely blamed on armed gangs from rival political parties, three more people were gunned down overnight. Pakistan's biggest city Karachi is virtually shut down. Many shops, schools and offices are closed and there is hardly any traffic on the streets. Most people are staying indoors fearing more violence. The Government says it has deployed an extra 1,000 troops. Pakistan Interior Minister Rehman Malik said that most of those who have been killed were innocent people. He said that 90 people have been arrested so far.Earlier on Friday, armed men attacked several houses with rockets and hurled hand grenades into the residential areas of Baldia town. Public transport, CNG and petrol pumps are closed in these areas.