The provincial Sindh government also deployed commandos and helicopters to conduct raids in Karachi, the main port city and the country's financial hub, where violence for four straight days left about 29 people dead, Pakistan's Daily Times reported.
"A semi-curfew will be imposed in some areas of Karachi," Pakistani Interior Minister Rehman Malik said Sunday following his meeting with top city officials.
The duration of the curfew would be decided by security agencies, the Press Trust of India reported. It said residents in curfew areas were asked to carry their identification cards at all times.
The Daily Times reported the violence has continued despite heightened security efforts.
The Urdu-speaking Muttahida Qaumi Movement, or MQM ,and the ethnic Pashtoon Awami National Party, known as the ANP, have blamed each other for the killings although both are members in the ruling coalition led by the Pakistan People's Party.
Malik was quoted as saying both parties are deeply concerned "and are in consensus to expose the elements hatching conspiracies against the government."
The News International quoted a provincial ANP official as saying only a military operation can resolve the problem.
Karachi has been gripped by ethnic and political killings for about a year and hundreds have died. The city's woes are separate from the widespread militant violence in other parts of the country.