The US Monday said a "significant" number of those behind the 9/11 attacks in New York are hiding in Pakistan and Washington was looking for "additional information that would lead us to them".
"With respect to the location of those who were part of the planning and execution of the attack of 9/11 against our country, we firmly believe that a significant number of them are in the border area of Pakistan," US Secretary of State Hillary Clinton said here.
She was addressing a joint press conference with External Affairs Minister S M Krishna after holding talks that covered wide-ranging issues, including terrorism emanating from the region.
Clinton, who was replying to a question, said the US has already conveyed this to Pakistan government.
"We are actively looking for additional information that would lead us to them," she added.
Pakistan has been denying that Al-Qaida chief Osama bin Laden or his senior lieutenants are hiding in its territory.
On an American soldier being kidnapped in Afghanistan, Clinton expressed concern over it and said the US was "working to do all we can to obtain his safe release".
The kidnappers recently released a video in which the soldier is shown in captivity.
Clinton asserted that the international security forces in Afghanistan were committed to defeat Taliban and other extremists despite such incidents.
"This is a very difficult battle but the one which must be waged."