Police in Pakistan's largest city, Karachi, have ordered shoot on sight after at least 98 people were killed in street violence in the last three days.
"We have issued orders to the security forces to shoot anyone involved in violence on the spot," Sharjeel Memon, the provincial information minister, told the Reuters news agency on Friday.
"In addition to the police and Rangers, another 1,000 personnel of the Frontier Constabulary will be deployed in the city to control the violence," he said.
Yusuf Raza Gilani, the Pakistan prime minister, appealed for peace on Friday, calling for the country to unite against the city's violence.
A police spokesman said 157 people had been arrested in the operation since Friday night, and 38 pistols and three AK-47 rifles recovered.
A paramilitary Rangers spokesperson said troops had rescued hundreds of people trapped in the troubled areas since Friday night.
"We have moved several families to safer places, and this exercise is continuing at the moment as well. The number of people evacuated so far is in the hundreds," he said.
According to police data, up to 98 people have been killed since the violence began on Tuesday, while more than 150 people have been wounded.
Shops and fuel stations were shut and public transport idled after Karachi's main political party Muttahida Qaumi Movement, which resigned from the federal government last week, called for a day of mourning.
The violence, which broke out in Orangi Town, later spread to Lyari, Baldia Town, Site and Gulshan-i-Iqbal areas.
Shooting could be heard in several areas on Friday, and in some spots residents burned tyres and threw stones at the few passing vehicles on the street.
At least 10 passengers were killed and 20 others injured on Wednesday when armed men opened fire on two buses in the port city, officials said.
The fresh wave of violence in the city began on Tuesday.
Karachi, home to more than 18 million people, has a long history of ethnic, religious and sectarian violence.
A recent report from the Human Rights Commission of Pakistan said 1,138 people were killed in Karachi in the first six months of 2011, of whom 490 were victims of political, ethnic and sectarian violence.
The US embassy in Islamabad released a statement from Cameron Munter, the US ambassador to Pakistan, condemning the violence.
"We call on all parties to refrain from further violence and work toward a peaceful resolution of differences," the statement read.
According to officials, Karachi contributes 68 per cent of the government's total revenue and 25 per cent of country's GDP.