Authorities appealed for calm Tuesday after a bombing against a Shiite Muslim procession killed 43 in Pakistan's largest city of Karachi, setting off riots and igniting fears of sectarian unrest.
Security was tight as thousands of people gathered in central Karachi for funerals of some of those killed in Monday's bombing of a Shiite procession marking the key holy day of Ashoura.
The attack sparked riots as people rampaged through the city, setting fire to markets and stores, including the port city's largest wholesale market. More than 200 firefighters were still battling the flames 24 hours after the attack, with authorities calling for reinforcements from the city of Hyderabad, 170 kilometers (105 miles) north of Karachi, Pakistan's main commercial hub.
Two buildings with dozens of shops and offices have already collapsed and two more were in danger of falling, said the Karachi fire chief, Ehteshamul Haq.
Pakistani officials blamed unnamed "miscreants" for the violence after the attack rather than Shiites involved in the procession, possibly in an attempt to temper sectarian tensions.
"We believe that it was a planned conspiracy," said Interior Minister Rehman Malik. "Those who went violent were miscreants and not the protesters."
It remained unclear who was behind Monday's bombing, at the start of a procession of Shiites marking Ashoura, the most important day of a monthlong mourning period for the seventh-century death of the Prophet Muhammad's grandson, Imam Hussein. Minority Shiites in Pakistan have suffered frequent attacks by Sunni extremist groups who regard them as heretical.
Karachi has largely been spared the Taliban-linked violence that has struck much of the rest of the country, a fact that analysts believe is driven by the group's tendency to use the teeming metropolis as a place to rest and raise money. But the city has been the scene of frequent ethnic, political and sectarian violence.
Bomb disposal squad official Munir Sheikh said some 35 pounds (16 kilograms) of high explosive were used in the bombing. He said the intact head and torso of the suspected suicide bomber was found on the third floor of a nearby office building, where it had crashed through a window.
Residents in apartments near the blast site tossed down body parts that had been cast into their homes from the explosion, while birds dove down to pick at the flesh amid damaged vehicles and motorbikes.
Senior health official Hashim Raza said the death toll increased to 43 on Tuesday. Many among the dozens wounded were critically hurt, and several died overnight and on Tuesday morning.
No group claimed responsibility for the attack, but Malik on Monday pointed his finger at a cluster of militant groups, including the Pakistani Taliban, al-Qaida, Lashkar-e-Jhangvi and Jaish-e-Mohammad, that he said have a joint goal to destabilize Pakistan.
Pakistani authorities say sectarian groups have teamed up with Taliban and al-Qaida militants waging war against the government in a joint effort to destabilize Pakistan. More than 500 people have been killed in attacks since mid-October when the army launched a major anti-Taliban offensive in the country's northwest.
Malik, who visited Karachi on Tuesday, said authorities were still trying to determine whether the attack had been carried out by a suicide bomber, as he had said Monday.
"The investigation is still going on to determine whether it was a suicide attack or some improvised explosive device was used," said Malik, who appealed for calm and said he had ordered an investigation into who was behind the rioting.
"If anyone is trying to cripple Karachi, then he is also trying to cripple Pakistan," the minister said.
Karachi Mayor Mustafa Kamal said that hundreds of shops had been destroyed, with damages estimated to run into millions of dollars.
Malik said a joint committee consisting of police, intelligence agencies and local business people has been set up to determine the cause of the rampage and the extent of the losses.
Malik appealed to the Shiite community to cancel processions for the next two days.
Monday's bombing was the third explosion in as many days to hit Karachi, although authorities attributed a blast that wounded 30 on Sunday to a buildup of gas in a sewage pipe. Protests broke out after that blast too, with Shiites torching at least three vehicles.
On Saturday, another blast near a Shiite procession wounded 19 people.
Associated Press Writer Munir Ahmad in Islamabad contributed to this report.