Video footage shows the lorry burning moments before the blast [AFP]

Investigators in Pakistan are sifting through the remains of Islamabad's Marriott hotel searching for clues as to who was behind the weekend's suicide lorry-bomb attack that killed at least 53 people and injured hundreds more.

Pakistanis and US intelligence officials said the attack bore the hallmarks of al-Qaeda, or an affiliate group, but no group has yet claimed responsibility.

"It was an al-Qaeda-style bombing and was similar to the attack on the Federal Investigation Agency office," a senior Pakistani investigator said, referring to a suicide attack in March in the eastern city of Lahore which left 20 people dead.

On Sunday, video footage was released showing the bomb-laden lorry drawing up to the security checkpoint some 20 metres from the hotel entrance.

The video shows the cab of the lorry on fire and small explosions as the flames take hold.

A security guard then approaches with a fire extinguisher in an effort to douse the blaze.

Moments later the picture freezes as the truck detonates, shredding through the front of the hotel and leaving a massive crater in the road outside.

The blast was so powerful that buildings several kilometres away had their windows blown out.

Reward

Investigators are hunting for clues in the rubble [Reuters]

On Sunday, recovery teams searched the scorched remains of the hotel, saying they expected to find more bodies as they went.

The blast ruptured a gas pipe and started a fire that burned throughout much of the hotel for several hours.

At least 11 foreigners were killed in the attack, including two American military personnel attached to the US embassy and the Czech ambassador, Ivo Zdarek.

The Pakistani government has offered a reward of $1.6m for any information that leads to those behind the bombing.

On Sunday, Yousuf Raza Gilani, Pakistan's prime minister, said the attack was an attempt to "destabilise democracy" in the country, which emerged from nine years of military rule earlier this year.

Speaking to Al Jazeera, Pakistan's information minister, Sherry Rehman, said the government was "mobilised on all fronts" to fight its own war against political violence, but faced a "borderless, amorphous" enemy.

"[It] is very difficult to locate and fight this war because there is really no location and no front," she said.

'Cancer'

The hotel bombing came shortly after Asif Ali Zardari, Pakistan's new president, delivered his inaugural address to parliament only a few hundred metres away.

Zardari's administration faces a struggle against al-Qaeda and pro-Taliban fighters in the country's northern tribal regions.

"Terrorism is a cancer in Pakistan, we are determined, God willing, we will rid the country of this cancer," Zardari said in a televised address to the nation. "We will not be deterred by these cowards."

Zardari has since left Pakistan for a scheduled meeting with George Bush, the US president, ahead of the UN general assembly meeting in New York this week.

The US administration condemned the "terrorist bombing" saying it was "part of a continuing assault on the people of Pakistan".

The Islamabad Marriott hotel, part of an American-owned chain, was a popular gathering place for foreigners and Pakistan's elite.

The attack appeared to have been timed to cause the maximum number of casualties, coming as the hotel was busy with families having their evening meal to break the Ramadan fast.

Marriott staff said about 1,000 people were staying in the hotel at the time of the attack.