KABUL, Afghanistan — Pockets of al-Qaida militants will endure in Afghanistan beyond next year's departure of most Western combat forces, but they have lost the ability to mount serious attacks of the kind that triggered the Afghan war, a senior U.S. commander said.

Major-General Joseph Osterman, the deputy operations chief of Afghanistan's NATO-led force, said small numbers of al-Qaida fighters remained entrenched in the rugged eastern mountain province of Nuristan, where the forested terrain and plunging valleys provided natural havens.

"They are less than 100, I would say, and they are in fact just trying to survive at this point," Osterman told Reuters in an interview late on Thursday. "I think what you find is that it's not necessarily that they have got a springboard in there."

Both Afghan security forces and NATO commanders have been keen to talk up gains in the 12-year battle against the Taliban and its insurgent allies, pushed from power by the U.S.-backed Northern Alliance following the al-Qaida attacks on U.S. targets on Sept. 11, 2001.

But isolated Nuristan, alongside Pakistan and straddled by the Hindu Kush mountains, has been something of a void for NATO forces, although al-Qaida and allies have used it as a conduit for attacks on Kabul and nearby provinces like Nangarhar and Laghman.

While NATO occasionally says it has killed al-Qaida commanders or "facilitators" in the province, most recently in May, Afghan commanders say some districts in the province are at risk of falling completely into militant control.

The former U.S. and NATO commander in Afghanistan, General Stanley McChrystal, in 2010 ordered American troops out of Nuristan, although special forces still operate there alongside thinly stretched Afghan forces, as well as anti-Taliban militias in the main villages of Kamdesh and Barg-e-Matal.

Armed U.S. drone aircraft also carry on strikes against insurgents there, although the number of attacks by drones has fallen off amid concern about civilian casualties.

"They continue to push against these guys and they continue to kill them, and really keep them from being a viable entity," said Osterman, a Marine commander who first came to the country as part of a U.S. military surge in 2010.

It is not clear if the presence of al-Qaida militants could derail efforts to bring the Taliban into talks in the Gulf state of Qatar, given U.S demands that the insurgent leadership renounce all ties to al-Qaida.

Osterman said in Nuristan, which has almost no roads or infrastructure, al-Qaida had become almost indistinguishable from the Taliban and other groups like Hizb-i-Islami Gulbuddin.

"They have been up there for a while, so they have inter-married with some of the population," he said.

"It's one of those things where they do have some local support in that regard. But it's not necessarily support for al-Qaida or support for the Taliban, in as much as they have been up there long enough that they have perhaps been accepted by some of the people."