A CCTV footage of the truck (right) after the explosion at the gate of the Marriott Hotel in Islamabad on Saturday. (AP)

Islamabad, Sept. 21 (Agencies): Video footage was released today showing the last moments before a truck laden with 600kg of explosives blew up outside Islamabad’s Marriott Hotel, killing at least 53 people and wounding more than 260.

“The truck was stopped at the barrier and there was an altercation between the attacker and the guards,” Rehman Malik, a top official in the interior ministry, which released the images, told a news conference.

“A doctor was on an emergency call and was standing behind the truck. He asked the guards to remove the truck so that he could drive in to attend a patient,” Malik said.

Sniffer dogs then detected something and guards shouted to people to run.

The footage showed the truck driver tried to ram the retractable metal barrier and bar at the security checkpoint at the entrance to the hotel’s forecourt and parking area.

Some accounts given earlier had suggested that there had been an exchange of fire between the truck driver and the security guards on duty, but that wasn’t clearly evident from the closed-circuit television images.

Most of the guards retreated when the truck tried to ram the barrier.

What happened next appeared to have been a small explosion in the cabin.

Flames were seen spreading from the front to the rear of the hydraulic dumper truck as cars passed by on the road behind.

After the explosion some guards moved in before retreating once again, and finally one came back with a fire extinguisher, but failed to stop the blaze.

Then the screen turned blue, presumably as the final explosion let rip, killing immediate bystanders. Other victims were felled by flying glass and from the subsequent fire that swept through the building.

Malik said he expected the investigation to point to the tribal areas used as bases by Taliban and al Qaida fighters on the border with Afghanistan.

Prime Minister Yousaf Raja Gilani said the bomber succeeded in bringing the truck into the high-security area in the guise of carrying construction materials.

“The terrorists want to end the democratic process and destabilise the country. They want to cause economic losses to the country and demoralise the security agencies.... The people should be vigilant to foil the designs of the terrorists,” Gilani said.

The intense heat radiating from the ruins of the Marriott Hotel was one clue to the scale of the destruction.

Dressed in masks and chemical-protection suits, rescue workers looking for survivors could not get very far inside the building.

Even 18 hours after the attack, the heat was too powerful and the building too unstable.

The explosion ignited gas cylinders in the kitchen, sparking a blaze that raced through the hotel. Some people leapt to their deaths from the upper floors rather than be burnt alive.

As rescue teams and firemen tried to go about their work, an eerie silence hung about the site.

The hotel, so heavily guarded that it was one of only two venues that many diplomats were allowed to frequent after a bombing at an Italian restaurant earlier this year, now looks more like a war zone.

Bits of human flesh are scattered outside the perimeter. Journalists have been kept away because authorities fear the building, not much more now than a burnt-out shell, could collapse.

Rows of cars outside the popular venue have been incinerated. Giant trees along the street are split in two, and the entrance to the hotel is little more than an enormous crater.

Security staff killed

The entire security staff manning the heavily fortified gate of the Marriott Hotel were among the 53 killed in the suicide bomb attack, a senior executive of the US luxury hotel chain said today.

“We put a very high premium on security at Marriott,” chairman and CEO of Marriott International, Bill Marriott said in a statement.