A huge truck bomb exploded at the entrance to the Marriott Hotel in Islamabad on Saturday evening, killing at least 40 people and wounding more than 150, according to the Inspector General of Police.

The blast, one of the worst terrorist attacks in Pakistan's history, went off just a few hundred yards from the prime minister's house, where all the leaders of government were dining after the president's address to Parliament.

The toll was expected to grow because of reports that many people had been trapped inside the six-story hotel, which has been a favorite meeting spot of both foreigners and well-connected Pakistanis in the heart of the capital. The building was quickly engulfed in flames and continued to burn for hours Saturday night.

The bomb left a vast crater, some 40 feet wide and 5 feet deep, at the security barrier to the hotel. Witnesses said security guards and their gate posts were buried under a mound of rubble. A line of cars across the street from the hotel were mangled and trees on the street were charred. Windows in buildings hundreds of yards away were shattered .