Troops have been deployed to put down a riot in the Pakistani city of Sialkot which broke out after an attack on a mosque which killed at least 30 people.
The attack took place during Friday's prayers
Shias set fire to public buildings, as a funeral took place for those killed in the suspected suicide bombing.
President Pervez Musharraf vowed to root out those behind the attack, saying "terrorists have no religion and are enemies of mankind".
The rioters set fire to the mayor's office and a police station in Sialkot.
A crowd of about 2,000 people carrying guns and iron rods looted the offices of Pakistan International Airlines and a state-owned bank, said witnesses.
"The army is handing the situation, but violence is still going on," said Mohammed Irfan, a police official.
Security was also tightened in other Pakistani cities.
Troops were called in to keep order
In Sialkot on Saturday, about 15,000 mourners gathered for the victims of the mosque bombings.
They chanted incantations while the local business community announced shops would close for two days in protest at the killings.
Meanwhile, police continued to search for clues at the mosque.
Officials said the identity of the bomber is still unknown but that 29 of the victims had been identified.
Witnesses reported seeing the attacker walk into the mosque with a briefcase, which when he opened, apparently set off the blast.
PAKISTAN'S SECTARIAN DIVIDE
Shias revere Ali, son-in-law of the Prophet Mohammed
Pakistan is 20% Shia, 70% Sunni
Violence between Sunni and Shia factions began in early 1980s
More than 150 people have died in the past year alone
About 4,000 people have been killed in total
Most violence takes place in Sindh, Balochistan and Punjab
The attack took place in the centre of the prayer hall, causing chaos.
"I was praying when I first saw a bright light and then something exploded with a big bang, and I fell down," said Sajjad Anwar, 36, who was being treated at a hospital.
"My mind stopped working for a while after the blast, but when I opened my eyes, I was lying among dead bodies," said Mumtaz Ali Shah, 43.
A second bomb weighing about 5kg was found in a briefcase but was defused by a bomb disposal squad.
No group has said it carried out Friday's blast.
The attack came almost a week after forces killed leading Sunni militant Amjad Farooqi which led to speculation the bombing was linked to his death.
Farooqi was wanted in connection with assassination attempts on Pakistan's president and the murder of US reporter Daniel Pearl.
About 100 Shias have been killed in sectarian clashes in Pakistan in 2004.
But correspondents says Sialkot is not a known centre for sectarian violence.
At least 20 people were killed in a suicide bombing on a Shia mosque in Karachi in May.
That attack followed the killing of a leading Sunni cleric.