The death toll from a bomb blast that ripped through an illegal gambling den in Karachi rose to 19 on Friday, with more than 40 other people wounded, officials said.
It was not yet clear if the explosion, that hit the city's largest gambling complex, the Rummy Club, was a criminal act or caused by religious extremists in the teeming violence-plagued city, a senior home ministry official told AFP.
"Three more people died of their injuries in hospital overnight, bringing the toll to 19," the ministry's Sharfuddin Memon said, adding that more than 40 people were receiving hospital treatment with three in a critical condition.
"We are investigating if the attack was the result of rivalry between criminal gangs or if some vigilante groups of extremists were involved," Memon said.
Hospital official Saleem Ahmed confirmed the casualty figures.
The city houses many clandestine gambling dens, which are officially outlawed in the Islamic nation and subject to occasional police raids.
Police said the bomb was small, made of two kilogrammes (four pounds) of explosives, but casualties were high because the gambling hall was crowded at the time.
Karachi is Pakistan's economic hub, home to its stock exchange and a lifeline for a depressed economy wilting under inflation and stagnating foreign investment.
But the sprawling city, with a population of 16 million, is plagued by ethnic and sectarian killings, crime and kidnappings.
Karachi is also politically tense and steeped in rivalries between the Urdu-speaking majority and an influx of ethnic Pashtuns from the northwest, which has been hit by a Taliban insurgency.
Outbreaks of political violence there killed more than 150 people last year and extremists targeted Shiite and Sufi religious gatherings, although attacks on government security forces in Karachi have been rare.
More than 40 people were killed over 18 days in March, officials said, amid heightened tensions between the Muttahida Qaumi Movement (MQM), which represents Urdu-speakers originally from India, and the Awami National Party (ANP), backed by Pashto-speakers.
The MQM and the ANP are partners in the Pakistan People's Party-led coalition that rules the southern province of Sindh, of which Karachi is the capital.
The violence came just a few hours after Pakistan's army had vowed to defeat terrorism and rejected US accusations of Islamabad "not doing enough" to combat Islamic militants in its northwest tribal belt.