ISLAMABAD, Pakistan, Sept. 21 -- Pakistani officials said Sunday that 21 foreigners, including two Americans stationed at the U.S. Embassy, were among the victims of a massive suicide truck bombing Saturday night that destroyed a luxury Marriott hotel in the capital.
Prime Minister Yousaf Raza Gillani said the bomber's intended target was Gillani's official residence a block from the hotel, where newly elected President Asif Ali Zardari and other officials were gathered to break their daily Ramadan fast when the bomb exploded about 8 p.m.
"The purpose was to destabilize democracy," Gillani said.
As rescue teams combed the still-smoldering five-story building, officials put the death toll at 53, with an unknown number of people unaccounted for. At least 266 people were injured. Most of the victims were hotel workers.
A spokesman for the Pentagon in Washington said Sunday that the two Americans killed in the blast were members of the U.S. defense forces assigned to the U.S. Embassy here. Their names were not released.
Pakistani officials said a contingent of 30 U.S. Marines was thought to be staying in the 290-room hotel.
A senior government security adviser, Rehman Malik, pointed the finger at Islamist militant groups based in South Waziristan, a volatile tribal area near the border with Afghanistan. These groups have vowed to retaliate against the government for stepped-up military raids and for a series of U.S. military incursions in pursuit of al-Qaeda and Taliban fighters.
"All roads lead to South Waziristan and Tehrik-e-Taliban," Malik said, referring to a militant group headed by Baitullah Mehsud, who has repeatedly vowed to attack the government after a truce with his forces collapsed last year.
Malik showed journalists a dramatic video of the attack, in which a large dump truck rammed into a metal barrier near the hotel and caught fire. The video showed guards scattering, trying to put out the blaze, and scattering again when the driver kept going, detonating the huge blast.
Marriott said in a statement Saturday that several hotel guards who had gone out to examine the truck were among the dead.
The truck had been packed with 1,300 pounds of military explosives, mortars and other weapons, Malik said. The bombing was timed to coincide with the fast-breaking meal, when guards were eating and likely to be distracted.
Malik said the attack was intended to destroy the hotel, a center of social and political life in the Pakistani capital and a frequent choice of foreign visitors. The ambassador from the Czech Republic was among the dead, officials said.
The hotel shortly after the explosion. 
CCTV footage has been released showing a truck bomb exploding outside the Marriott Hotel in Islamabad, Pakistan. The footage shows a camera, which was manually controlled to focus specifically on the developments as they happened.

The nearly four minutes of footage, shows a large truck pulling up in front of the hotel at a guarded gate. After the truck attempted to ram through the barrier, some reports stated that guards began to fire shots into the truck.

"The truck was stopped at the barrier and there was an altercation between the attacker and the guards," said Pakistani Interior Ministry official Rehman Malik in a statement to the press.

Guards began to run away once the truck slammed into the gates, but began to approach the truck seconds later. The cabin of the truck then explodes sending sparks and debris in all directions, with some of it hitting the camera. The truck begins to catch fire and people can be seen returning to the scene in an attempt to put out the blaze. Unsuccessful, the truck explodes, taking the camera out with it.

Officials believe al-Qaeda is responsible for the attack which killed 53 people and injured almost 300. Rescuers are searching for survivors, as an unknown number of people are still missing. At least 21 of those killed were from foreign countries.

Officials say the target was aimed for a residence a block away which was said to be housing Asif Ali Zardari, Pakistan's new prime minister. He was attending a dinner with several other Pakistani officials.