At least 30 people have been killed after a bomber struck a procession of Shia in the southern Pakistani city of Karachi, according to police sources.
The explosion struck on Monday as Shia worshippers marked Ashoura.
Police sources told Al Jazeera that at least 80 people were injured in the blast, with many of those in a critical condition.
The attack sparked riots in Karachi with angry mourners throwing stones at ambulances, torching cars and shops and firing bullets into the air.
The Pakistan Rangers, a paramilitary force, took control of several restive areas of Karachi after the blast, officials said.
Rehman Malik, the interior minister, called for people to show restraint and asked that Shia processions over the next two days be cancelled following the attack.
Television footage showed crowds around the blast area, smoke rising over the scene and ambulances going back and forth.
"I fell down when the bomb went off with a big bang," Naseem Raza, a 26 year-old who was marching in the procession, told The Associated Press news agency.
"I saw walls stained with blood and splashed with human flesh."
Fazal Qureshi, the chief editor of the Pakistan Press International news agency, told Al Jazeera: "These processions cover long distances, they were marching through the central road when suddenly the bomber blew himself up.
"It is impossible to stop someone who is prepared to die. There is an atmosphere of fear throughout the city."
Bomber tackled
Major Aurangzeb Khan, a spokesman for the paramilitary troops who were protecting the procession, said the death toll would have been much higher if one of the soldiers had not spotted the bomber and tackled him.
"He just took him down, and the bomber detonated himself," he said.
Authorities found the intact head and torso of the suicide bomber on the third floor of a nearby office building, where it had broken through a window, Munir Sheikh, a bomb disposal squad official, said.
About 16kg of high explosive were used in the bombing, he said.
Pakistan had tightened security to protect mass processions ahead of Ashoura, deploying tens of thousands of police and paramilitary forces.
PHOTO CAPTION
A security official arrives at the scene after a bomb attack on a procession of Shia commemorating Ashura in Karachi December 28, 2009.
Agencies