People carry the body of a shooting victim for a funeral in Karachi, Pakistan, as violence over the last four days has claimed the lives of more than 50 people. (Shakil Adil/Associated Press)

Parts of Pakistan's largest city shut down Wednesday after an attack on a scrapyard pushed to 51 the number of people killed in four days.

Some shops were set on fire in an outlying neighbourhood of Karachi, where police tried to calm gathering crowds, footage broadcast on Pakistani TV stations showed.

Karachi, a port city of 16 million, has a long history of political, ethnic and religious strife, but this year has been exceptionally bloody.

As of June, around 300 "targeted killings" had occurred in the city, roughly twice that of 2009. Many of the slayings in Karachi have been linked to gangs allegedly controlled by political parties. The wave of violence in the city has coincided with Sunday's election to replace a provincial lawmaker killed in August.

In the latest attack, gunmen opened fire in the scrapyard, which was in a commercial market area, killing 11 people late Tuesday. The dead included eight Pakistanis of Baluch descent, said Sharmila Farooqi, a provincial government spokeswoman.

Farooqi said most of the killings in recent days were politically motivated, and some of the 55 suspects detained by police in connection with the violence were linked to political parties.

Security forces were patrolling the city to prevent fresh violence Wednesday, said Farooqi. In many neighbourhoods, businesses shut down, while public transportation was scarce.

"The atmosphere of terror is everywhere," said local resident Mohammad Sadiq. "People are scared to come out of their houses."

Shops on fire

Footage on Pakistani TV showed several small shops, including fruit and vegetable stalls, ablaze in Malir, a neighbourhood on the outskirts of the city. Young men ran onto the streets, and police officers tried to keep the situation under control, the footage showed.

Prime Minister Yousuf Raza Gilani declared that culprits would be punished, but said officials had not discussed whether to deploy army soldiers to the city. Whether to involve the powerful army is a question that routinely arises when violence spikes in Karachi.

"I think the civilian authorities will manage," Gilani 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 Talibanization of the city, a jab at the Awami National Party, which represents the ethnic Pashtuns from the Taliban heartland in the northwest.

Election boycott

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 Haider's seat, but the ANP announced 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 faulted 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 Wednesday, a police constable was wounded when someone threw a grenade at a checkpoint on the outskirts of Pakistan's main northwestern city, Peshawar, said Liaquat Ali, a senior police official. Peshawar is right on the edge of Pakistan's tribal belt, a lawless stretch of territory along the Afghan border where many militants shelter.