Pakistani security forces have been ordered to shoot on sight when confronting disorders in Karachi, where days of political and ethnic violence have left up to 85 people dead.
About 1,000 additional police and paramilitary forces were deployed in Karachi on Friday with new orders to shoot any armed "miscreants" they encounter.
Interior Minister Rehman Malik told reporters that dozens of suspects have been detained in connection with a series of targeted killings since Monday. At least 34 people died on Thursday alone when gunmen opened fire on buses.
Police say the killings are part of clashes between political groups in Sindh province, including the Muttahida Qaumi Movement and its rival, the Awami National Party (ANP).
The MQM largely represents the Urdu-speaking community, and until last month was part of the ruling coalition in Sindh. ANP represents ethnic Pashtuns. Both those groups and the ruling Pakistan People's Party are believed to have links to armed groups in Karachi.
Shops were closed and streets were deserted in the southern port city Friday after the MQM called for a day of mourning and protest rallies.
MQM leader Raza Haroon has said his movement's supporters are being targeted because the party quit the coalition.
The Human Rights Commission of Pakistan says 490 people were victims of targeted killings in Karachi in the first half of this year.
On Friday, Pakistani Prime Minister Yousuf Raza Gilani appealed for peace and security in Karachi, saying it was important for the economic development of the country.
U.S. Ambassador to Pakistan Cameron Munter called on all parties to refrain from further violence and work toward a "peaceful resolution of differences."
Amnesty International criticized the government's order for security forces to "shoot on sight" armed men involved in the violence. The rights group said Friday that by giving troops such power the government is effectively declaring Karachi "a war zone" and encouraging further lawlessness and violence, citing what it said was the army's record of human rights violations.
About 18 million people live in Karachi, the country's economic hub. The city also has been the scene of sectarian violence between Sunni and Shi'ite Muslims and militant attacks.
Meanwhile, in Pakistan's northwest, military officials say troops backed by jets have killed 11 militants in the Kurram tribal region along the Afghan border. Officials say nearly 50 militants have been killed in Kurram since a military operation began there this week.