Pakistan shows CCTV footage of Marriott bombing

ISLAMABAD (Reuters) - Video footage was released on Sunday showing the last moments before a truck laden with 600 kg 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," said Rehman Malik, the 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 continued.

Sniffer dogs then detected something wrong 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 make an impression on 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 Qaeda fighters on the border with Afghanistan.

"Preliminary investigations revealed that 600 kg explosives were used," Malik said. "High explosives RDX and TNT were used."

"Unlike previous attacks, aluminum powder was also used... When the fire balls hit the building, the aluminum powder fueled the fire," he said, explaining the ferocity of the blaze.

(Writing by Simon Cameron-Moore; Editing by Matthew Jones)