SAN'A, Yemen—In nearly a decade of rebuilding its terror network here, al Qaeda has put down deep roots, a move that is now complicating U.S.-backed efforts to battle the group.

Unlike other chapters of the global terror network, Yemen's Al Qaeda in the Arabian Peninsula is a largely homegrown movement, with carefully cultivated ties to the local population. That sets it apart from other affiliates of al Qaeda, and could make it much more difficult to dislodge.

The group's strategy: apply lessons learned from mistakes by affiliates in other Mideast havens, particularly Iraq and Saudi Arabia.

In both those places, al Qaeda's footprint weakened significantly as local support for the group turned sharply against it. To avoid a similar fate in Yemen, the group has worked hard to curry favor with local tribes—so much so that it is now largely interwoven in the country's tribal fabric.

"They've worked hard to put deep, and what they hope are lasting, roots that will make it very difficult for them to be rooted out of Yemen," says Gregory Johnsen, a Yemen expert at Princeton University. "They've done a good job of looking at the mistakes that other versions of al Qaeda have made elsewhere."

Since late last year, Yemen has emerged as one of the biggest and most dangerous hubs for al Qaeda operations. U.S. officials have tied al Qaeda militants based here to two attacks against U.S. targets, including the attempted Christmas Day airline bombing allegedly by Nigerian Umar Farouk Abdulmutallab, who told U.S. Officials that he received his training from al Qaeda operatives in the Arab country. The push into Yemen, say U.S. officials, shows the group's increased ability to wage jihad against the U.S. and its allies, a main al Qaeda goal.

In recent months, a top al Qaeda leader publicized moving his foreign family here, while another married into a local tribe. The group is providing social and financial assistance in some of the country's poorest areas, according to tribesmen, local residents and a former al Qaeda member. Its leaders have also tempered its message of global jihad to fit local grievances—including the lack of economic benefits from Yemen's oil revenues—to recruit new members.

In exchange, some tribal leaders are welcoming al Qaeda members, allowing their sons to sign up, and providing protection from government troops. That has made al Qaeda militants almost indistinguishable from many of the rugged tribesmen and sympathizers they now mix with.

"As long as Qaeda respects the tribes, some tribes will welcome them," says Sheikh Abdulqawi Sherif, the head of the pro-government Bani Dhabian tribe, whose land borders Mareb and Shebwa provinces, two areas where al Qaeda cells are based.

Gen. Yahya Saleh, nephew of Yemen's president and the head of one of the country's counterterrorism forces, acknowledges the alliances some tribes have with al Qaeda.

Still, he says, "the tribes in Yemen are practical. They know there will be a heavy price to pay for harboring al Qaeda, and more and more, [the tribes] will not be willing to pay that price."

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