Shahzad says he received training in bomb-making in Waziristan, part of the Federally Administered Tribal Areas, known as the FATA.

Last month, I traveled to Peshawar, the gateway to Pakistan's rough tribal areas along the border with Afghanistan, and a city that the failed Times Square bomber, Faisal Shahzad, visited in July.

Shahzad says he received training in bomb-making in Waziristan, part of the Federally Administered Tribal Areas, known as the FATA. This region has become jihadi central — the reputed base of al-Qaeda, and the headquarters of the tough Afghan Taliban Haqqani network; the Pakistani Taliban; groups of Arab, Uzbek and Chechen militants; and Pakistani groups that fought in Kashmir. These groups are increasingly interconnected.

Pakistan's military cleared the country's own Taliban out of South Waziristan and other parts of the FATA. But it has been reluctant to mount an offensive in North Waziristan, where many of the toughest jihadis are now gathered. Shahzad's near miss is a vivid reminder that Pakistan needs to finish the job.

We don't yet know whom Shahzad met in Waziristan or who trained him. The Pakistani Taliban, which has killed thousands of its own people with suicide bombs and has threatened U.S. cities, claimed credit for the Times Square attack, although there is no proof this is true. But Shahzad's travels to the region are one more indication that it has become a magnet for individuals who want to learn how to carry out terrorist attacks against the West.

Several European plots were hatched in the area, and other would-be American attackers found help there. Najibullah Zazi, the Afghan-American who plotted to blow up New York subways, trained in Waziristan, as did David Headley, the Pakistani-American from Philadelphia who helped prepare the 2009 terrorist outrage in Mumbai; and Bryant Neal Vinas, an American who plotted an attack on U.S. railways. Five northern Virginia terrorist wannabes tried to go there before being captured elsewhere in Pakistan.

Over the past year, the Pakistani military abandoned its previous reluctance to tackle militants in the tribal areas. The switch occurred after the Pakistani Taliban reneged on a previous peace deal in the valley of Swat, turning the public against them, and after local Taliban began inflicting terrible casualties on Pakistani civilians and military forces.

Yet even as leading militants fled other parts of the FATA for North Waziristan, Pakistan's military brass insisted they wouldn't mount a frontal offensive there. Some critics contend they're reluctant because they want to use the Haqqani network of Afghan Taliban as a bargaining chip in future peace talks in Kabul. But the military insists it is too stretched to attack North Waziristan, and it has a reasonable case.

My conversations in Pakistan last month convinced me, however, that this attitude is changing — for reasons of self-interest. The Shahzad factor is likely to accelerate the timing of a new offensive.

"Pakistan will have to do it sooner or later," said retired Brigadier Mahmood Shah, formerly in charge of security in the tribal areas. He recalled how, at a dinner for a retiring commander, he heard senior military officers saying, "Pakistan will have to bite the bullet in Northern Waziristan and go in for a roller-coaster operation like we did in Swat."

Shah told me, "At present, they are doing limited ground operations and search-and-destroy operations" in North Waziristan. But he added that "there is no escaping" the need for a full-scale offensive.

Besides the arrest of Shahzad, there are other recent events that will impel the military to act. First is the recent reemergence of Pakistani Taliban leader Hakimullah Mehsud in a video, months after reports of his death in a U.S. drone strike. The video threatened attacks on the United States.

Second is the danger that militants based in North Waziristan could provoke a war with India. On Monday, the lone survivor among the Pakistani terrorists who attacked Mumbai was found guilty. Another such attack could push India to military action.

Although Pakistan's intelligence chief denies prior knowledge of the Mumbai attack, the groups trained by Pakistan to fight India in Kashmir are still active, with fragments said to be based in Waziristan. There are indications that Shahzad may have had contacts with one of those groups, Jaish-e-Muhammad. An associate of his was arrested just after prayers at a Karachi mosque known for its links with the group.

Add up all these elements, and it becomes clear that Pakistan will have to clear North Waziristan of jihadis who threaten its basic interests. The United States should offer Pakistan all cooperation in this endeavor, including close coordination across the border in Afghanistan. There's no time to lose.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. Readers may write to her at: Philadelphia Inquirer, P.O. Box 8263, Philadelphia, Pa. 19101, or by e-mail at trubin@phillynews.com.