Two US marines were among the four foreigners killed in the devastating suicide attack on the Marriott hotel in Islamabad [Images] as rescue workers on Monday completed the search of the gutted multi-storied luxury hotel, saying there was no possibility of finding any more survivors.

A suicide bomber rammed a truck packed with 600 kg of military grade explosives into the main gate of the Marriott on Saturday evening killing 53 people.

A US embassy official in Islamabad confirmed that the two employees of the US defence department were among the dead and that a third American, who was a contractor for the state department, was unaccounted for.

He said three other US embassy employees and a contractor were injured. The bomb attack also claimed the life of the Czech ambassador to Pakistan.

The hotel was packed with foreigners and Pakistanis who had gathered for the iftar meal to break the traditional fast during the holy month of Ramzan when the attack took place.

A total of 266 people were injured in the attack, described as the biggest bombing ever in Pakistan's history.

Rescue workers on Monday said they had completed their search in most parts of the five-storey, 290-room hotel that was a favourite gathering spot for Westerners and the Pakistani elite. They said there was no possibility of any more bodies being found in the blackened structure.

On Sunday, some eight to 10 bodies were pulled out of the building, including that of Czech Envoy Ivo Zdarek.

Engineers said only the upper part of the hotel was affected by the blast.

They said its structure and foundation were "solid and safe" and ruled out the possibility of building's collapse.

Earlier, officials said they had feared the structure might collapse after being ravaged by the powerful explosion and the subsequent fire.

Forensic experts too carried out an assessment of the structure. Investigators have also gathered clues at the site of the blast over the past two days.

Authorities on Sunday released security camera footage of the attack, including the final minutes before the massive explosion that was heard up to 30 km away.

Officials said the truck was packed with aluminium powder, a highly flammable material that accelerated the fire in the hotel.

Geo News channel quoted sources as saying that the interior ministry had obtained footage from security cameras installed in four locations at the hotel. The clearest footage was obtained from the camera that overlooked the main gate.

This footage showed the face of the suicide bomber and the main blast, which occurred about four minutes after the bomber blew himself up in a small explosion.