Suspected gang members have killed 39 people in two days in Pakistan's largest city, with many of the victims tortured, shot and stuffed in sacks which were dumped on the streets, officials said today.
The gangs are allegedly affiliated with Karachi's main political parties and have been blamed for a surge in killings in recent months.
The government has been unable to stop the violence, as it is also grappling with a faltering economy and a raging Islamist insurgency.
The unrest illustrates the precarious state of Pakistan's stability at a time when the US wants the nuclear-armed country to step up its fight against Taliban militants who stage cross-border attacks against foreign troops in Afghanistan.
Seventeen people were killed in Karachi yesterday and another 22 today, said Saud Mirza, police chief in the teeming metropolis of some 18 million people. Many of the victims were tortured, shot in the head and stuffed in burlap sacks, he said.
A resident in one of the neighbourhoods which has experienced much of the violence said people were afraid to leave their homes.
The latest round of violence seemed to be driven by a mix of political and criminal motivations, said Sharfuddin Memon, security adviser to the government in Sindh province, of which Karachi is the capital.
"Gangs operating in the city are involved in the fresh killing," he said. "They are kidnapping people for different reasons, torturing and killing."
A senior leader of the most powerful political party in Karachi, the Muttahida Qaumi Movement, blamed some members of the ruling Pakistan People's Party for the recent violence.
Raza Haroon claimed the killings were being carried out by a committee set up by the PPP to control violence in Lyari Town, a poor area and ruling party stronghold.
"Now the gangs have so much courage that they have started killing Urdu-speaking people ruthlessly," he said.
A large number of Muttahida Qaumi Movement's supporters are Urdu-speaking descendants of people who came to Karachi from India soon after the birth of Pakistan in 1947.
"We demand the government stop this horrible genocide of Urdu-speaking people," Mr Haroon said.
Sharjeel Memon, Sindh's information minister and a senior member of the PPP, declined to respond to the allegations. He said the chief minister of the province would hold a press conference later.
Supporters of the PPP have been targeted by the violence as well.
A former national politician from the ruling party, Waja Kareem Dad, was gunned down yesterday evening, according to security adviser Mr Memon.
The recent violence came after the Muttahida Qaumi Movement left the federal coalition led by the PPP in late June and joined the opposition.
Karachi has a long history of political, ethnic and sectarian violence, but the recent wave is high by historical standards. More than 300 people were killed in July alone.
There were at least 490 political, ethnic and sectarian killings in Karachi during the first half of the year, among more than 1,100 killings overall in that time period, according to the Human Rights Commission of Pakistan.
There has also been violence in Pakistan's north-west tribal regions along the Afghan border, where the Taliban and other militants have bases.
Pakistani army chief General Ashfaq Parvez Kayani announced today that an operation in the Kurram tribal region had ended in success. The military operation there has killed more than 200 militants since July, officials said. The UN has said thousands of civilians were displaced.
The army has staged multiple operations in nearly all parts of the tribal belt to push out insurgents, but with limited success. The army has declared victory in various operations, only to resume fighting later when militants regroup.