ISLAMABAD — A decade after the 9/11 attacks, most international terrorist plots against the West have links to Pakistan, the country that became al Qaida's most important sanctuary after the United States chased the terrorist group from Afghanistan.

Pakistan wasn't considered an international terrorist haven before December 2001, when Osama bin Laden crossed the White Mountains from Tora Bora, his last redoubt in Afghanistan, into Pakistan's tribal area.

In the nearly 10 years since, however, the country has become al Qaida's global headquarters, infecting Pakistan's Islamic extremist groups with a new nihilistic ideology and transforming the country's tribal area near the border with Afghanistan into the epicenter of global jihad, a violent sanctuary where the traditional population is terrorized and al Qaida and other terrorists plot attacks not just against the West and U.S.-led forces in Afghanistan but also against the Pakistani government itself.

Analysts say that U.S. officials, distracted by the war in Iraq, didn't recognize until 2008 the danger that was developing in Pakistan, after which they began hugely ramping up their campaign of pilotless drone airstrikes in the tribal area.

U.S. officials now claim that al Qaida is close to what Defense Secretary Leon Panetta calls "strategic defeat." But while there have been no successful al Qaida attacks in the West since the London transit system was bombed on July 7, 2005, Islamic extremist attacks are frequent and deadly in Pakistan, a failing nuclear-armed country of 180 million people.

Earlier this week, at least 25 people were killed in a twin suicide bombing in the western city of Quetta that targeted the local deputy commander of Pakistan's paramilitary Frontier Corps. It was the latest in some 260 suicide bombings that have struck Pakistan since 2001.

Al Qaida has developed a crucial relationship with Pakistan's most ferocious local terrorist group, Tehreek-i-Taliban Pakistan, often known as the Pakistani Taliban, which is based in the tribal areas, where federal authority traditionally has been limited. Without this group, al Qaida might not survive.

"For al Qaida to survive, can it afford to lose Pakistan? Of course not," said Noman Benotman, a former Libyan jihadist who once worked with the al Qaida leadership. "The problem now is that the Pakistani Taliban and al Qaida work very closely together."

"The Pakistani Taliban is like the sea and al Qaida is like fish. To swim, they need the sea," said Benotman, who's now a senior analyst at the Quilliam Foundation, a London-based anti-extremist campaigning organization.

Al Qaida "central" has been badly weakened in Pakistan. American drone strikes have killed 24 mid- and senior-level commanders of the core organization since January 2008, including two men then considered to be number three in the leadership, Abu Laith al Libi in 2008 and Mustafa Abu al Yazid last year, according to a tally kept by New America Foundation, an independent research organization in Washington. Last month, a drone strike killed al Qaida's new deputy chief, Atiyah Abd al Rahman.

Pakistani authorities, often working with the CIA, have arrested a host of al Qaida commanders, including the self-confessed mastermind of the 9/11 attacks, Khalid Sheikh Mohammed, captured from the northwest city of Rawalpindi in 2003, another third in command, Abu Faraj al Libi, from Rawalpindi in 2005, and this year Umar Patek, an Indonesian militant said to be behind the 2002 Bali bombing.