At least 60 persons were killed and more than 200 injured in what was described as the biggest suicide attack that virtually devastated the entire building of the capital’s main Marriott Hotel on Saturday.

The blast took place about three hours after President Asif Zardari delivered his maiden address to the joint session of Parliament less than a km from the scene of the explosion.

The authorities said the truck used in the blast first tried to break through the heavily barricaded Constitution Avenue on which key government buildings, including the Parliament House, the Presidency and the Prime Minister’s House, are located. The suicide bomber then turned back and blew himself up in the Marriott Hotel building.

The army was also called out from the twin city of Rawalpindi to help the rescue teams that were trying to extinguish the fire and retrieve the dead and injured from the debris. Several foreigners staying in the hotel were either wounded or were still buried under the debris.

The Saudi envoy told reporters that 16 Saudi nationals were staying in the hotel, many of whom had been injured. “Six are missing and we are trying to locate them in hospitals or the debris.”

About 1,000 kg of explosive was used in the attack and is reported to be the heaviest in scores of bomb blasts in the recent years. The impact was felt miles away from the scene of the blast. Several buildings adjacent to the hotel and across the road, including the Frontier House and Evacuee Property Trust Building, were also badly damaged. Houses of ministers in the Ministers Colony, near the Frontier House, were also damaged.

Adviser (interior) Rehman Malik said a high-level investigation team comprising experts from security agencies had been constituted to probe the explosion. Malik said several policemen and security guards also lost their lives.

A spokesman for the Indian High Commission said no Indians were present in the hotel at the time of one of the worst terror attacks in the country.

A senior Pakistani journalist, who was staying in the hotel and narrowly escaped the attack, believes there were two blasts within about seven minutes.

“I heard the blast in my room on the fifth floor of the main hotel building and came out to find out what had happened, as the hotel reception was not responding,” says Imtiaz Alam, eminent columnist and secretary-general of the prestigious South Asia Free Media Association (SAFMA).

Imtiaz took the elevator when he heard a bigger bang. The elevator also caught fire and was badly damaged by the time it slid down to the next floor.

“With great effort I was able to open the door and darted out seconds before the lift fell down with a big thud”, Imtiaz said. In front of the door and all around debris had piled up and some of it was on fire. A live electricity cable was also burning while water and gas had filled the corridor.

“I saw men, women and children bleeding and screaming for help that was no at hand. They were groping in darkness for the exit to the stairs”, he said. Imtiaz and a Sri Lankan guest succeeded in locating the stairs after several minutes and led the guests to the ground floor and out of the building.

Karim, who drives an ambulance, said he saw a small car banging the barrier on the main hotel gate. A young fellow emerged from the car and shouted: “I warn everybody here to run for his life.” The car sped in no time and another ‘dumber truck’ appeared within three minutes, broke through the barrier and then exploded with a big bang.

Security agencies were forewarned on Friday of a possible suicide attack on Parliament House on the occasion of the presidential address or the iftar reception hosted by speaker of the National Assembly Dr Fahmida Mirza, officials here said.

The authorities had beefed up security and deployed heavy contingents of paramilitary Rangers, besides police. The speaker this morning shifted the venue of the reception to the nearby Prime Minister’s House, which felt severe impact of the blast.

There was confusion and scare among the guests, who included President Asif Zardari, Prime Minister Yousaf Raza Gilani, ministers, MPs, senior civil and military officials. While security agents shifted the top leadership to the basement in the Prime Minister’s House, other guests took shelter around various parts of the building.