PESHAWAR, Pakistan — Almost three years ago, Sajjad Khan used to buy supplies for the Pakistani Taliban with U.S. dollars that he says came from al-Qaida.

Now he realizes what al-Qaida is getting in exchange. Khan's 13-year-old nephew has been pulled from a madrassa to train as a suicide bomber, and Khan fears he himself might be killed for begging the boy not to go.

"The Taliban come in secret and take them for training from the madrassa," said Khan, a burly, black-bearded Pashtun, holding a picture of his young nephew. "They go to the Taliban but they get their training from the Arabs. It all comes from al-Qaida."

Al-Qaida's influence runs like a thread through the myriad of militant groups on the Pakistani border — it ties the groups together, yet is often hard to discern. The hidden nature of al-Qaida's presence makes it harder for the U.S. and Pakistan to fight, especially when the two countries disagree on which groups pose the greatest threat.

"Al-Qaida is strictly behind the scenes — as a force multiplier, providing training, expertise both in combat arms and propaganda," says Bruce Hoffman, terrorism expert at Georgetown University in Washington.

The groups are wildly disparate and their relationships increasingly complex. They range from the tribal homegrown Taliban to an Afghan father-and-son team where the father, Jalaluddin Haqqani, once visited the White House and met U.S. President Ronald Reagan. Experts say some groups are virtually fronts for al-Qaida, but others have a tenuous relationship that might be limited to ideology.

"The problem is that these groups are overlapping more and more, the layers of allegiances are hard to peel away, and the greater interconnectivity makes it quite hard to know what is really happening in any given conflict," says Daniel Markey, a regional expert at the New York-based Council on Foreign Relations.

For example, in closed-door sessions over the past two weeks, Pakistani lawmakers have discussed whether they should make a distinction between the local Taliban and al-Qaida and enter talks with the Taliban. However, the two groups appear to be increasingly connected.

Deep within the warren of rickety book stalls in the old city of Peshawar, book sellers are hawking a version of al-Qaida's military training manual translated into Pashto, a local language. A copy obtained by the AP featured instructions on suicide bombings and on what chemical compounds cause the greatest damage in explosives.

"The distribution of the manual attests to the Taliban's growing strength and organizational capabilities," states the U.S. Military's Counter Terrorism Center (CTC) at West Point, N.Y. "Already into its fourth edition, there is clearly a demand among Taliban cadres for the lessons outlined in the manual."

The Tehrik-e-Taliban Pakistan, as it is known, is led by the ailing Baitullah Mehsud, who is accused of masterminding last year's assassination of opposition leader Benazir Bhutto. It brings together some of Pakistan's most violent militants, including Faqir Mohammed, a close ally of al-Qaida's No. 2 Ayman al-Zawahari, and Maulvi Fazlullah, whose long-haired, gun-toting followers have terrorized Pakistan's Swat Valley.

Al-Qaida's training is showing up in increasingly audacious suicide bombings and more sophisticated attacks within Pakistan and Afghanistan, where the Taliban-led insurgency is claiming more U.S. lives almost by the day.

In the past, militants usually targeted troops and convoys in the volatile northwest, where some 100,000 Pakistani forces are deployed. But in the last year they have taken their battle nationwide, striking hundreds of miles from the lawless border regions.

Last November a suicide bomber blew up an Air Force bus in Sargodha, about 125 miles south of the nation's capital of Islamabad. In early March a powerful suicide truck bomb nearly toppled a seven-story police headquarters in Pakistan's eastern Punjab city of Lahore, barely 24 miles from the Indian border. And a September truck bombing devastated a five-star hotel in the heart of Islamabad and killed 53 people.

Former Taliban members told the AP that al-Qaida is now financing local movements even in regions beyond the tribal belt and training recruits from the thousands of madrassas or religious schools that flourish in northwest Pakistan.

"Now the sort of sophistication al-Qaida had in terms of terrorism, they have started passing it on to the Taliban," said Mehmood Shah, former security chief for the border regions. "The Taliban that ruled Afghanistan were village mullahs, not very smart, but they have changed, they have evolved and today they are stronger and smarter because of al-Qaida's training."

The difficulty of knowing who is linked to al-Qaida is clear in the case of Maulvi Naseer, a leader of a branch Taliban group. Pakistan hailed Naseer for killing or driving out hundreds of al-Qaida-linked Uzbeks from the tribal regions close to the Afghan border last year. More than 200 were killed, and many others found shelter with the Tehrik-e-Taliban.

But despite Naseer's seeming distance from al-Qaida affiliates, the U.S. says he sends his fellow tribesmen across the border to fight U.S. troops there. Naseer has said he will not attack Pakistan but considers Afghanistan the site of a holy war because foreigners are killing Muslims there.

The U.S. badgered Pakistan to take action against Naseer without success. In July, the U.S. took the law into its own hands and launched a missile strike into Naseer's village, killing six people but missing him, according to media reports.

Al-Qaida's influence is also complicating Pakistan's relationship with the militant groups on its border.

Some jihadi groups, such as Lashkar-e-Tayyaba, have long been seen as creations of Pakistan's intelligence service to help wage its clandestine war against India in disputed Kashmir. Pakistan's intelligence also has a three-decades-long history with the Haqqanis, the father and son blamed by the U.S. for the deadly bombing of the Indian Embassy in Kabul in July and the assassination attempt earlier this year on Afghan president Hamid Karzai.

"Pakistan doesn't view it in its interest to strike all or even most of these groups. Several have been useful proxy organizations for Pakistan in Afghanistan, Pakistan itself and India," says Seth Jones, an analyst with the U.S. based RAND Corporation.

However, others say Pakistan's control over the militants slipped away after last year's military assault on an extremist mosque in the heart of the Pakistani capital of Islamabad. The July army offensive against militants who had taken over the Red Mosque drew Pakistan into a deadly spiral of increasingly violent and vicious attacks by groups within Tehrik-e-Taliban.

Some say it was al-Qaida that launched the militants on the warpath against Pakistan.

"Al-Qaida, which had been targeted by the Pakistani (security officials), convinced Baitullah Mehsud to turn against Pakistan," said Brian Glyn Williams, associate professor of Islamic history at the University of Massachusetts. "Pakistan's Frankenstein had turned on it with a vengeance. Its hands-off policy had boomeranged back to hit them."