Pakistan army troops arrive Sunday to conduct a rescue operation at the site of Saturday's massive truck bombing at Marriott hotel in Islamabad, Pakistan. (AP Photo/Anjum Naveed)

Rescuers pulled more bodies from the shell of the truck-bombed Marriott Hotel in Pakistan's capital Sunday, pushing the number of people killed to 53, including the Czech ambassador to Pakistan.

Ambassador Ivo Zdarek was among at least 21 foreigners who died when a suicide bomber driving a dump truck crashed through security gates and detonated explosives in front of the building. The blast injured more than 250 people.

Interior Ministry chief Rehman Malik said two Americans were confirmed dead as well as one Vietnamese national. Officials in Pakistan said other foreigners in the group included people from Britain, Germany and the Middle East. There are no known Canadian casualties.

The hotel, a favourite spot for foreigners and the Pakistani elite — and a previous target of militants — still smouldered from a fire that raged for hours after Saturday's explosion.

Officials said the main building could still collapse. Malik Ashraf Awan, a senior civil defence officer, said the building's structure is unsafe because of the shock and heat.

The bomb went off close to 8 p.m., when four restaurants inside would have been packed with diners, including Muslims breaking their daily fast during the holy month of Ramadan.

Prime Minister Yousuf Raza Gilani said the bomber attacked the hotel only after tight security prevented him from reaching parliament or the prime minister's office, where the president and many dignitaries were gathered for dinner.

No group immediately claimed responsibility, though suspicion fell on al-Qaeda and the Pakistani Taliban. Analysts said the attack served as a warning from Islamic militants to Pakistan's new civilian leadership to stop co-operating with the U.S.-led war on terror.

The U.S. military has intensified missile strikes against suspected militant hideouts along Pakistan's border with Afghanistan in recent weeks.