Dramatic footage from a devasting attack on Islamabad's Marriott Hotel which killed at least 53 people suggests that the death toll could have been far worse if the bomber had been able to ram his truck through a security barrier.

More than 250 people were injured in the blast, which officials and investigators immediately blamed on an al-Qaeda affiliate operating out of a tribal area near the Afghan border. They included six Britons, one of them a minor.

Four foreigners were killed: the Czech ambassador, his Vietnamese partner and two Americans.

The six-wheeled truck, designed to resemble a construction vehicle, was carrying an estimated 600kg of high explosives mixed with incendiary aluminum powder.

Had the driver managed to ram his way into the lobby, that would have been enough to destroy the five-storey hotel popular with businessmen, diplomats and journalists.

But CCTV footage broadcast on Pakistan television showed that the driver was unable to ram through security barriers and could not persuade the guards to let down the final barrier. Instead he blew himself up.

The main blast followed several minutes later, while guards were trying to put out the original fire and persuade those in the hotel to flee. There was no footage of that blast because it destroyed the camera filming the front of the hotel.

The blast ignited gas cylinders in the kitchen, setting off a blaze that swept through the 300-room hotel. A security official said some victims leapt to their deaths rather than be burnt alive on the upper floors.

Last night's bombing came just hours after Asif Ali Zardari, Benazir Bhutto's widower, gave his inaugural presidential address to Parliament, vowing to stamp and terrorism. It also coincided with the first anniversary of Osama bin Laden's call for Pakistani Muslims to jihad or holy war against their government, a vital ally in the US-led War on Terror.

The attack appeared to have been timed to inflict maximum casualties, ripping through the hotel when it was packed with families having dinner to break the daily fast in the Muslim holy month of Ramadan. The hotel is also popular with Westerners.

Pieces of human flesh were still scattered outside the hotel this morning. The intense heat inside kept rescuers, who were wearing masks and chemical protection suits, from getting inside most of the destroyed building.

A senior security official said at least 60 people were dead. The government put the confirmed toll at 53. Bodies pulled from the debris were burnt beyond recognition.

The bombing is a serious challenge to Mr Zardari, who faces a desperate battle against al-Qaeda and Taleban militants whose campaign of violence has killed 1,300 people in Pakistan this year.

“We will rid the country of this cancer,” Mr Zardari, who took office less than two weeks ago, said in a message to the nation after the attack.“I appeal to all democratic forces to come and save Pakistan."

But analysts say the ability to carry out such a massive bombing at one of the most secure sites in the capital, not far from Parliament and the Prime Minister’s residence, is an unmistakable sign of the militants’ reach.

Mr Zardari’s predecessor Pervez Musharraf turned Pakistan into a close ally of the United States after the September 11 attacks in 2001, and the Government has waged a crackdown on militants in Pakistan’s volatile northwest. That campaign has drawn the ire of many in Pakistan, the world’s only nuclear-armed Islamic nation, and critics say elements of the army and intelligence services are supporting the militants.

Many militants poured into the northwest tribal areas from across the border in

Afghanistan when the United States invaded after 9/11, and much of the region is now effectively outside the Pakistani government’s control. Recent cross-border raids by US forces based in Afghanistan - condemned even by Mr Zardari is unacceptable - have increased tensions.

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