The United States has said it would step in if Pakistan failed to root out Taliban sanctuaries.

Terrorists still "base, train and operate from that country's (Pakistan's) territory," US Ambassador to Afghanistan Zalmay Khalilzad said on Monday. "We cannot allow this problem to fester indefinitely.

"Unless Pakistan roots out Taliban sanctuaries, it will be difficult to fully eliminate security problems in the south and east of Afghanistan," he told the Centre for Strategic and International Studies, a major think tank in Washington, DC.

"We have told the Pakistani leadership that either they solve this problem or we will have to do it ourselves. We prefer that Pakistan takes the responsibility, and the Pakistan government agrees," he said.

In Islamabad, foreign office acting spokesman Abbas Jilani said the remarks were "uncalled for and unwanted".

Jilani said Khalilzad was not aware of the US' stand on Pakistan's role against terror.

The US had always appreciated Pakistan's efforts in eliminating and rooting terrorist infrastructure, Jilani said, adding that statements like the one by the US envoy might lead to problems.

Pakistan Information Minister Sheikh Rashid Ahmed also rejected the envoy's warning. "The United States must realise ground realities," the state-run PTV quoted Rashid as saying.

"We will deal with terrorists on our homeland," Rashid said adding, "Pakistan does not need foreign forces to act on our soil and Pakistan will not allow anybody for such action."