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Aamir Qureshi/AFP/Getty Images
Pakistani bystanders and rescue workers are seen beside a huge crater outside the burning facade of The Marriott Hotel in Islamabad today following a powerful bomb blast.

ISLAMABAD, Pakistan — A massive suicide truck bomb devastated the heavily guarded Marriott Hotel in Pakistan's capital Saturday, killing at least 40 people and wounding at least 250. Officials feared there were dozens more dead inside the burning building.

The blast targeting the U.S. hotel chain appeared to be one of the largest terrorist attacks ever in Pakistan, leaving a vast crater some 30 feet deep in front of the main building, where rescuers ferried a stream of bloodied bodies.

The five-story Marriott had been a favorite place for foreigners as well as Pakistani politicians and business people to stay and socialize in Islamabad despite repeated militant attacks.

The bombing came just hours after President Asif Ali Zardari made his first address to Parliament and days ahead of the new leader's meeting with President Bush Tuesday in New York on the sidelines of the U.N. General Assembly.

Rehman Malik, the head of Pakistan's Interior Ministry, told The Associated Press that authorities had received intelligence that there might be militant activity due to Zardari's inaugural address. Security had been tightened, he said.

Though there was no immediate claim of responsibility for the blast, Pakistani officials have warned that militancy could heat up following a wave of cross-border strikes on militant bases by U.S. forces in Afghanistan, which had angered public opinion.

IntelCenter, a group which monitors al-Qaida communications, said senior al-Qaida leader Mustafa Abu al-Yazid, who claimed the June Danish Embassy bombing in Islamabad, threatened additional attacks against Western interests in Pakistan in a video timed to the recent anniversary of the Sept. 11 attacks.

"This is terrorism and we have to fight it together as a nation," Malik told reporters at a hospital overflowing with the wounded.

The United States strongly condemned the attack.

"President Bush offers his sincere condolences to the families of all those lost in today's vicious attack," said Gordon Johndroe, a spokesman for the National Security Council at the White House. "This is a reminder of the threat we all face. The United States will stand with Pakistan's democratically elected government as they confront this challenge."

The hotel served as the headquarters for the international media during the 2001 war against the Taliban in neighboring Afghanistan. Its 258 rooms and popular health club stood in a plot surrounded by government office buildings less than a mile from the presidency and Parliament.

Witnesses and officials said a large truck had rammed the high metal gate of the hotel at about 8 p.m., when the hotel's restaurants would have been packed with diners, including Muslims breaking the Ramadan fast.

A U.S. State Department official led three colleagues through the rubble from the charred building, one of them bleeding heavily from a wound on the side of his head.

One of the four, who identified himself only as Tony, said they had begun moving toward the rear of the Chinese restaurant after a first, small blast and that a second explosion threw them against the back wall.

"Then we saw a big truck coming to the gates," he said. "After that it was just smoke and darkness."

Mohammed Asghar, a worker from a nearby office with a makeshift bandage round his head, said there was more than one man in the truck and that they had argued with the hotel guards.

"Then there was a flash of light, the truck caught fire and then exploded with an enormous bang," he said.

Mohammad Sultan, a hotel employee, said he was in the lobby when something exploded. He fell down and everything temporarily went dark. "I didn't understand what it was, but it was like the world is finished," he said.

Senior police official Asghar Raza Gardaizi said rescuers had counted at least 40 bodies at the scene and that he feared that there "dozens more dead inside."

Associated Press reporters saw at least nine bodies scattered at the scene. Scores of people, including foreigners, were running out — some of them stained with blood.

Information Minister Sherry Rehman said 250 people were wounded. Two hospitals said 10 foreigners were among those in their treatment, including one each from Germany, Saudi Arabia, Morocco and Afghanistan.

U.S. Embassy spokesman Lou Fintor said officials were trying to account for embassy staff and any other Americans affected. He said he had no other details.

Ambulances rushed to the area, picking their way through the charred carcasses of vehicles that had been in the street outside. Windows in buildings hundreds of yards away were shattered. Tropical fish from the tanks inside lay among the torn furnishings in the entrance area.

Marriott said it was working with rescue personnel and local authorities to aid the victims.

"We live in a dangerous world and this is a terrible tragedy. We grieve for those people who died, or were injured, and their families," Bill Marriott, chairman and CEO of Marriott International, said in a statement.

In January 2007, a security guard blocked a suicide bomber who triggered a blast just outside the Marriott, killing the guard and wounding seven other people.

Pakistan has faced a wave of militant violence in recent months following army-led offensives against insurgents in its border regions, including several in the capital.

In July, a suicide bombing killed at least 18 people, most of them security forces, and wounded dozens in Islamabad as supporters of the Red Mosque gathered nearby to mark the anniversary of the military siege on the militant stronghold.

In June, a suicide car bomber killed at least six people near the Danish Embassy in Islamabad. A statement attributed to al-Qaida took responsibility for that blast, believed to have targeted Denmark over the publication of cartoons depicting the Prophet Muhammad.

In mid-March, a bomb explosion at an Italian restaurant killed a Turkish woman in the capital, and wounded 12 others, including four FBI officials.

Associated Press writers Zarar Khan, Stephen Graham, Munir Ahmad and Nahal Toosi in Islamabad contributed to this report.