The US defence department chose to sidestep queries on whether it had the authority to carry out unilateral action against Taliban or al Qaeda leadership on Pakistani soil but pressed Islamabad to "move rapidly" against the militants in its restive tribal areas.

"I'm comfortable, as the military leader, that I have all the authorities I need....I'm not going to get into the specifics of it," chairman of the Joint Chiefs of Staff

Admiral Mike Mullen told reporters amid reports that the US had secured President Pervez Musharraf's [Images] nod to go after Osama Bin Laden without prior permission from Islamabad.

Mullen was asked whether the US had the authority to operate in the Federally Administered Tribal Areas (FATA) against bin Laden or other al Qaeda leaders and Taliban leaders based on actionable intelligence without seeking Pakistan's consent.

"This also is a sovereign country, and we just don't send troops into sovereign countries, as the question suggests. So I think it's important that our assistance be as robust as it can possibly be and that the Pakistan government and military move as rapidly as they can against this problem," Mullen said.

The top Pentagon official said the United States and the NATO forces were deeply concerned at the escalating violence in Afghanistan and were evaluating steps that are necessary to counter the resurgent Taliban.

"I am, and have been for some time now, deeply troubled by the increasing violence there. The Taliban and their supporters have, without question, grown more effective

and more aggressive in recent weeks, and as the casualty figures clearly demonstrate," Mullen said.

"The United States and NATO leadership -- and I had the chance to meet with my NATO counterparts last week in Brussels -- are very focused on the challenges there, particularly in the east and the south," Mullen said.

He said he was ready to fly in more US troops to Afghanistan but "those forces will not be available unless or until the situation in Iraq permits us to do so."

 "It's a very complex problem, and it's tied to the drug trade, a faltering economy and, as  I've said many times, the porous border region with Pakistan. There's no easy  solution, and there will be no quick fix.

"More troops are necessary, and some of our NATO allies have recently committed to sending more of their own, but they won't fully ever be sufficient," he added.