Gunmen have opened fire in a commercial market in Karachi, killing 11 people and raising the death toll from political violence to 51, a Pakistani official said.
Last night's attack is the latest in a spasm of violence to rock Karachi and underscore the poor state of security in the US allied nation.
At least 51 people, including several political activists, have been killed in the city since Saturday.
Because of its status as the country's main economic hub, keeping Karachi calm is of prime importance to Pakistani leaders who have already seen criminal activity soar alongside Taliban-led Islamist militant violence.
A major chunk of supplies for US and Nato troops is shipped to the city before travelling overland in Pakistan and into neighbouring Afghanistan.
The attack on the market occurred late last night and its victims included eight Pakistanis of Baluch descent, said Sharmila Farooqi, a provincial government spokeswoman.
The wave of violence in the city has coincided with Sunday's election to replace a provincial lawmaker killed in August.
Ms Farooqi said police had detained 55 suspects in connection with the latest violence, and that some were linked to local political parties. Security forces were patrolling the city to prevent fresh violence, she said.
The two parties most linked to violence in Karachi - the Muttahida Quami Movement and the Awami National Party - have their electoral bases in different ethnic groups that make up a large share of the city's population.
The MQM claims to represent the Urdu-speaking descendants of those people who came to Karachi from India soon after the birth of Pakistan in 1947. It is secular and likes to speak out against the so-called Talibanisation of the city, a jab at the Awami National Party, which represents the ethnic Pashtuns from the Taliban heartland in the north west.
Raza Haider, the member of the provincial assembly who was gunned down in August, was a senior member of the MQM.
Both parties were competing for Mr Haider's vacant seat, but the ANP announced on Saturday evening that it would boycott the election, saying the MQM would rig the vote. The MQM won the seat.
MQM lawmaker Haider Abbas Rizvi said the party had handed authorities a list of 150 alleged criminals it suspects in the attacks but that nothing had come of it. He not only blamed the ANP, but also the Pakistan People's Party, which control's the provincial government.
ANP spokesman Amin Khattak said the MQM was to blame, noting that the killings began shortly after his party said it would boycott the election.
Also today, a police constable was wounded when a grenade was thrown at a checkpoint on the outskirts of Pakistan's main north-western city, Peshawar, said Liaquat Ali, a senior police official. Peshawar is on the edge of Pakistan's tribal belt, a lawless stretch of territory along the Afghan border where many militants shelter.Reuse content