The city's major markets, stores and business centers were closed, along with financial institutions that had already planned to shut for New Year's Day. Public transportation was halted and gas stations were closed.

Monday's bombing occurred in the midst of a procession of minority Shiite Muslims during the Islamic holy month of Muharram. Afterward, angry protesters went on a rampage, setting fires to about 2,000 stores that took three days to completely put out.

Interior Minister Rehman Malik, on a visit to Karachi, said investigators were still determining if the attack was a suicide bombing.

He also questioned the claim of a purported Taliban spokesman, Asmatullah Shaheen, that the militant group was behind the attack. Local news reports on Friday quoted a more prominent Taliban spokesman, Azam Tariq, as denying that the Pakistani Taliban's central leadership had approved the attack, though he did not rule out the possibility that Shaheen's group had carried it out without approval.

Also Friday, a suspected US missile struck a car carrying alleged militants in North Waziristan tribal region, killing three men, two intelligence officials said. It was the second such strike in less than a day.

The strikes are part of the US campaign to eliminate high-value militant targets that use Pakistan as a safe haven to plan attacks in neighboring Afghanistan and on the West.

Friday's strike happened near Mir Ali, a major town in the region, two intelligence officials said on condition of anonymity because they were not authorized to speak on the record. Shortly afterward, Taliban fighters arrived at the scene of the attack in the village of Ghundi and moved the bodies to an undisclosed location, the officials said.

Thursday's missile strike was also near Mir Ali, hitting a house and killing three people.

US officials rarely discuss the strikes, and Pakistan publicly condemns them, though it is widely believed to aid them secretly.

Elsewhere in the northwest, a roadside bomb exploded near a car in the Bajur tribal region, killing an anti-Taliban tribal elder and five of his family members, said Nasib Shah, a local government official.

Bajur was the focus of a 2008-09 army offensive but still suffers some militant violence. Tribal leaders who support the government against the Taliban are frequent targets of attacks.