Islamabad, Pakistan ? U.S. special forces have begun teaching a Pakistani paramilitary unit how to fight the Taliban and al-Qaida, hoping to strengthen a key front-line force as violence surges on both sides of the border with Afghanistan.

The sensitive mission puts rare American boots on the ground in a key theater in the war against extremist groups, but it risks fanning anti-U.S. sentiment among Pakistani Muslims already angry over suspected CIA missile attacks on militants in the same frontier region.

Despite such complaints, the training program comes as some tribes in the frontier zone are setting up militias to help the Pakistani government combat extremist movements. The new forces have been compared to the Sunni Arab militias in Iraq that helped beat back the insurgency there.

Still, the U.S. training program is reportedly smaller than originally proposed and was delayed, apparently reflecting misgivings in Pakistan’s government about allowing U.S. troops on its territory.

Its start has not been officially announced, but a Pakistani military officer and a U.S. defense official told The Associated Press that two to three dozen trainers arrived earlier this month.

The Pakistani said the Americans had already begun training senior personnel of the paramilitary Frontier Corps at an undisclosed location in Pakistan’s restive northwest, adjacent to Afghanistan. He said the course included classroom and field exercises.

The Pentagon official said the Americans would stay for a few months. He said that it would likely be a one-time effort and that there were no plans to send more trainers.

Both agreed to discuss the program only if granted anonymity, because details had not been made public.

Asked about the program Thursday, Pentagon spokesman Bryan Whitman declined to give any specifics. But he contrasted the mission with much larger U.S. training efforts in Iraq and Afghanistan, where U.S. soldiers are embedded with local units on the battlefield.

“It is a train-the-trainer type of concept,” Whitman said. “They are not actually conducting operations.”

The Frontier Corps is a relic of British rule that was long a poorly armed, untrained police force that the government hopes can be remade into a potent unit capable of confronting Taliban militants.

Its troopers are local men, in contrast to the army, which is dominated by ethnic Punjabis and is viewed as an occupying force by the Pashtun tribes living on both sides of the border. U.S. and Pakistani officials argue that the corps’ local knowledge and cultural sensitivities make it the best tool in a battle where winning hearts and minds is crucial.

The goal is that a strong Frontier Corps can take on most combat duties, allowing a gradual pullback of the army that is hoped will ease tensions in the northwest.

The U.S. has poured some $10 billion into Pakistan since the then-president, Gen. Pervez Musharraf, turned against his former Taliban allies in Afghanistan after the Sept. 11 attack on the U.S. Most of the money has gone to the army, including the $70 million earmarked for the Frontier Corps program.

U.S. forces already trained Pakistan’s Special Services Group, a commando unit that crushed militants holding Islamabad’s Red Mosque last year. Washington also has supplied the helicopter gunships that are seeing heavy use in army offensives in several Pakistani border regions.

But with the war dragging in Afghanistan, U.S. lawmakers and commentators have questioned why Pakistan still seems unable to eradicate militant sanctuaries on its side of the border.

“This thought has come pretty late in the day,” Rasul Bakhsh Rais, a professor of political sciences, said of Pakistan’s decision to let the trainers in. “But still I don’t think it is too late, given the fact that this is going to be a very long war.”