A suicide bomber on Monday targeted Pakistan's largest procession of Shiite Muslims on their holiest day, killing at least 30 people and wounding dozens more in defiance of a major security crackdown. The blast sparked riots in Karachi, the financial capital, where angry mourners went on the rampage, throwing stones at ambulances, torching cars and shops and firing bullets into the air, sparking appeals for calm. Pakistan had deployed tens of thousands of police and paramilitary forces, fearing sectarian clashes or militant attacks on Ashura processions, when Shiites whip themselves to mourn the seventh-century killing of Imam Hussein. The latest bombing underscored the extent of the volatility in Pakistan, where militant attacks have killed more than 2,760 people since July 2007 and which Washington has put on the frontline of its war on Al-Qaeda. 'The blast was so huge that I felt my hearing had gone, but then I started hearing cries of injured people and saw pieces of human flesh and blood on the road,' said Abbas Ali, 35, one of the mourners thrown to the ground. Interior Minister Rehman Malik blamed Tehreek-e-Taliban, against which the military has been waging a major operation in near the Afghan border, and Lashkar-i-Jhangvi, another of Pakistan's most feared Islamist networks. 'At least 30 people have been killed so far in the suicide attack and 63 others have been injured,' provincial health minister Saghir Ahmed told selfnews. 'We have declared emergency at all hospitals in Karachi and doctors are making every effort to save the injured. The situation is very grim,' he added. Mohammad Ali Jinnah Road, where the attack happened, was ablaze with burning cars and motorcycles, and covered in debris from buildings attacked by rioters, said an selfnews correspondent. Firefighters battled helplessly to quench the flames engulfing buildings and shopkeepers stood crying outside their businesses going up in smoke. 'We are using our maximum resources available to put out the fire which is still raging in the markets,' said city mayor Mustafa Kamal. Karachi has escaped most of the bomb attacks that have battered the northwest and other major cities. Monday's attack was the deadliest in Karachi since a suicide bomber targeted the homecoming of former prime minister Benazir Bhutto -- who was assassinated two months later -- killing at least 139 people in October 2007. It was the third attack on Ashura commemorations in Pakistan this year. A suicide attack at a Shiite mosque in Pakistani-administered Kashmir on Sunday killed seven people. Explosives wounded 17 people in Karachi on the same day. Police said two suspects were arrested at the bomb site, and said a sketch of the bomber would be issued based on the discovery of his severed head. A spokesman for the paramilitary Rangers said one of their members died as he pinned down the suicide bomber, claiming that otherwise the blast would have inflicted far more casualties. 'Our soldier Abdul Razzaq spotted the suicide bomber and jumped on him and both fell to the road after which the bomber exploded himself,' spokesman Major Mohammad Aurangzeb told selfnews. More than 50,000 Shiites had marched in Karachi, wearing black or beating their naked torsos with chains and slicing their skin with knives. After the attack, furious mourners set ablaze dozens of shops and vehicles, beating up police and paramilitary Ranger personnel, witnesses said. Thick black smoke filled the sky and explosions of fuel tanks further panicked residents on Mohammad Ali Jinnah Road as ambulances raced to ferry casualties to hospital. Pakistan's Prime Minister Yusuf Raza Gilani and President Asif Ali Zardari condemned the latest blast and appealed to the masses to remain peaceful. Sectarian violence periodically flares in Pakistan between Shiites, who beat and whip themselves in religious fervour during Ashura, and the country's majority Sunnis, who oppose the public display of grief. Shiites account for about 20 percent of Pakistan's mostly Sunni Muslim population of 167 million. More than 4,000 people have died in outbreaks of sectarian violence in Pakistan since the late 1980s. 