ISLAMABAD, PAKISTAN - Two suicide bombers killed at least 64 people outside Pakistan's biggest weapons factory Thursday, in the deadliest attack by the Taliban since they began hitting Pakistani government sites with suicide bombers more than 18 months ago.

The Taliban said the bombings were in response to a fierce Pakistani military campaign that has unfolded over the past two weeks in the tribal region of Bajaur.

The insurgents warned of more attacks if the government continues its campaign.

Following the resignation of President Pervez Musharraf on Monday, the twin suicide bombings underscored the Taliban's determination to safeguard their strongholds in the lawless tribal areas, no matter who holds power in Islamabad.

Musharraf, who until December was army chief as well as president, was reviled by the militants, who at least twice tried to assassinate him, and was deeply unpopular with the public for sometimes using heavy force in the tribal regions. In response, the militants organized scores of suicide bombings in Pakistan last year.

The current civilian government, elected in February, promised negotiations in hopes of gaining a reprieve. Early this year the military struck fresh peace deals with the militants, pulling the army back from parts of the tribal regions. The fighting in Bajaur has been the most intense since then.

The attack Thursday was directed against the Pakistan Ordnance Factories, a complex about 20 miles north of the capital of more than 16 factories with about 20,000 workers. It seemed timed to cause maximum casualties, coming during the afternoon change of shifts.

The vivid displays of carnage pose one of the greatest challenges to any post-Musharraf government that might be willing to meet a U.S. demand for greater action against the militants, who have used the tribal areas to stage attacks on U.S. forces across the border in Afghanistan.

A retired general who headed the ordnance factory at Wah, Talat Masood, said that in choosing the weapons complex, the Taliban had deliberately selected a symbolically important industry, and one that Pakistanis thought was virtually impregnable.

The insurgents were also intent, Masood said, on trying to intimidate the four-month-old civilian government, which is already in deep disarray and has paid scant attention to the insurgency.

"They are trying to give a signal that they can hit at any defense installation," he said of the Taliban. "And they are intensifying the pressure on the civilian government to stop the Bajaur operation."

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