Tension has been high in Karachi for much of October Pakistan’s President Asif Ali Zardari has summoned two senior ministers to Islamabad to discuss continuing violence in the city of Karachi.
Mr Zardari’s meeting with Interior Minister Rehman Malik and Sindh Home Minister Zulfiqar Mirza comes a day after 25 people were killed by gunmen.
A day of mourning is being observed and funerals of the dead are being held.
Businesses are closed and public transport is off the roads. More than 50 people have died since Saturday.
Violence broke out over the weekend during a by-election for a provincial assembly seat that was held by local Muttahida Qaumi Movement (MQM) politician Raza Haider, who was murdered in August.
His death triggered riots that killed at least 100 in a city with a history of ethnic and sectarian tensions.
Hundreds of people have died in politically motivated attacks and militant bombings since January.
On Tuesday 12 people were killed in an attack on a car spare parts market. The rest died in a series of attacks elsewhere. All the dead are civilians.
The market is located in the south of Karachi, within walking distance of the city’s main dockyard.
Most shopkeepers in the area belong to the Urdu-speaking community that traditionally supports the MQM, which is part of the governing coalition in Sindh province.
The violence has pitted the MQM on one side and the Awami National Party (ANP) and the Pakistan People’s Party (PPP) – backed by the Pashtun and Balochi communities – on the other.
The MQM held onto Mr Haider’s seat. The ANP boycotted the by-election.
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