Hours ahead of President Barack Obama's crucial talks with his military chiefs, US Secretary of State Hillary Clinton has asserted America is not losing the war in Afghanistan, but acknowledged "the Taliban has momentum".

In significant comments before Obama unveils his new AfPak strategy, Clinton said the new approach would be "different".

"It's not going to be just a repeat of the same old approach, we're trying some different things," the Secretary of State said in an interview to ABC television from Pakistan, as Obama meets his top field commanders to weigh their suggestion of sending 40,000 more troops to Afghanistan.

"When the President makes his decision, that will be evident," she said.

She said the US was not losing the war in Afghanistan but acknowledged "Taliban has some momentum" at the moment.

In another interview to NBC television, Clinton said US presence in the troubled Afghanistan "is not an open-ended, never-ending commitment".

When asked whether there was a way out for America from the protracted battle, she replied "absolutely".

In the interview to ABC, Clinton defended her blunt remarks to Pakistan questioning its commitment to hunt top al-Qaeda leadership hiding inside the country.

"I think it would be a missed opportunity and lack of recognition of full extent of the threat if they did not realise that any safe haven, anywhere, for terrorists, threatens them, threatens us and has to be addressed," Clinton said.

She however, credited the Pakistan government for taking on the Taliban, saying: "I think they have gone after the enemies that most threaten them".