A bomb attack on a packed Shia mosque in the southern Pakistani city of Karachi has left at least 15 people dead, officials say.
Worshippers survey the devastation of Friday's attack
More than 100 other people were hurt, 25 of them critically, doctors said.
Hundreds of youths from the Shia Muslim minority went on the rampage after the attack, burning vehicles and an office.
Sindh province officials said the attack was a suicide bombing. President Pervez Musharraf branded it a "heinous act of terrorism".
He ordered an immediate investigation.
Officials believe the bombing was the work of extremists from the Sunni majority.
Provincial spokesman Salahuddin Haider said a suicide bomber had detonated explosives in the middle of the congregation.
The mosque, in Karachi's business district, was filled with scores of Shia worshippers attending Friday prayers.
Appeal for blood
The explosion occurred at around 1300 local time (0800 GMT). No one has yet said they carried out the attack.
The mosque was severely damaged, with blood stains marking the floor and walls and pieces of flesh scattered on the
The dead included the imam (prayer leader) of the mosque, Khawaja Kumail, officials said.
A worker at a nearby brokerage house told the Reuters news agency: "Our office on the 14th floor was shaken. We saw plumes of smoke, blood and bodies."
Another witness, Kalb e-Abbas, told the Associated Press: "I was inside the mosque for Friday prayers when a bomb exploded. Something hit my arm and I saw blood all over my body."
A state of emergency was declared at the main Civil Hospital where weeping relatives gathered amid scenes of chaos.
Vehicles drove around making appeals for blood donations.
Police cordoned off the mosque as angry locals besieged the area shouting abuse at officials and police officers.
People from both Sunni and Shia communities chanted slogans and youths hurled rocks.
The police said they were trying to avoid the use of force against the rioters and were in talks with local Shia leaders to try to control the situation.
The provincial government has announced it will give 100,000 rupees ($1,750) compensation to families of the dead and 30,000 rupees to each of the injured.
Provincial government adviser Aftab Sheikh said: "I condemn this attack; it was a barbaric act."
A Shia Muslim cleric, Hasan Turabi, said: "We are at the mercy of terrorists who are getting bolder
because they are not being punished. Now we have to defend ourselves."
The mosque is inside one of Pakistan's oldest and most famous educational establishments, the Sindh Madrassah-tul-Islam.
The establishment has separate mosques for Shias and Sunni Muslims.
Pakistan is 80% Sunni Muslim with the remainder Shia. The communities have a history of violence.
On 2 March, Sunni radicals killed more than 40 people and wounded 150 in an attack on a Shia procession in the south-western city of Quetta.
Last July an attack on a Shia mosque in Quetta left around 50 dead.