Pakistani security forces are on high alert a day after a suicide-bomb attack in the southern city of Karachi killed more than 50 people.
Businesses and schools across Karachi were closed and security forces patrolled largely empty streets, but there was isolated rioting for the second day to protest the bombing.
The provincial government has declared a three-day mourning period, while bracing for more possible attacks.
Hard-line religious groups are using the bombing Tuesday outside a Sunni Mosque to fuel anti-government sentiment.
Speaking to reporters, the president of the conservative MMA religious alliance, Qazi Hussain Ahmed, indirectly blamed the attack on Pakistan President Pervez Mushharaf.
"This is the proof of the failure of the government of Pervez Musharraf," he said. "They cannot provide protection."
No one has claimed responsibility for the attack, which ripped through a packed Sunni prayer meeting celebrating the Prophet Mohammed's birthday.
Local police say a single bomber staged the suicide attack, one of the worst ever in Karachi.
At least 57 people were killed, nearly 100 others injured. The attack sparked violent riots with furious mobs burning cars and clashing with local police.
Thousands of mourners attended funerals as officials struggled to determine who was behind the deadly bomb blast. The list of possible suspects includes everyone from Indian provocateurs to Islamic radicals.
Suspicion has also focused on Shi'ite militants, who frequently clash with their Sunni counterparts in Karachi. The city is a frequent battleground for the two Muslim groups, and there are growing fears of a sectarian backlash.
Suicide attacks in Pakistan are typically staged by religious extremists, and there have been a number of cases of the majority Sunnis and minority Shi'ites attacking each other in the city.
Earlier this year, a series of clashes between the two left more than 30 people dead and scores more seriously injured.