The top US military officer has said the border region between Afghanistan and Pakistan is still the world's most dangerous area, calling it the epicentre of terrorism.
In a BBC interview Adm Mike Mullen again called on Pakistan to end "safe havens" there.
Adm Mullen has been visiting US bases in southern and eastern Afghanistan.
The trip could be Adm Mullen's last to the region before he retires as chairman of the joint chiefs of staff.
Adm Mullen said his biggest worry, as he neared the end of his four-year tenure, was continued instability in Pakistan's tribal areas along the Afghan border.
He said that despite the death of Osama Bin Laden, plenty of bin Laden acolytes were still plotting operations beyond the region.
He has often raised this issue with senior Pakistani military leaders.
"Probably one of the things I've learned is that I'm a little bit more impatient and I'd like to see things happen more quickly," Adm Mullen said.
"Their patience level is such that sometimes we would disagree on time frames and the need to move now, but again that's a choice they get to make with their own forces, it doesn't mean we don't continue to address these issues."
Adm Mullen said Pakistan had lost many of its own troops taking action against some groups.
But he said that unless they moved against terrorists like the Afghan Haqqani network, it could affect relations between Washington and Islamabad.
He admitted relations were still very strained in the wake of the secret US raid in May that killed Osama bin Laden and embarrassed the Pakistan military.
But he said the answer was not to sever ties.
Pakistan has always made it clear it has its own strategic interests and approaches in the region.
Adm Mullen said he understood that, but in the long run he said a strategy of using proxies to foment violence had to change.
If instability worsened, it would, as he put it, be a real challenge for everyone.
