US secretary of state Hillary Clinton launched a scathing attack on Pakistan for failing to hunt down al Qaida inside its borders, saying the government knew where the terror leaders were hiding.
American officials have long said that al Qaida mastermind Osama bin Laden and senior lieutenants of the network accused over the September 11 2001 attacks operate out of the rugged terrain along the border with Afghanistan.
But Mrs Clinton's unusually blunt comments went further in asserting that Pakistan's government has done too little about it.
"I find it hard to believe that nobody in your government knows where they are and couldn't get them if they really wanted to," Mrs Clinton told Pakistani journalists in Lahore.
"Maybe that's the case. Maybe they're not gettable. I don't know."
There was no immediate reaction from Pakistani officials, but the thrust of Mrs Clinton's comments were startling, coming after months of lavish public comments from her and other American officials portraying Pakistan's leaders as finally receptive to the war against militants inside their own country.
As a political spouse, career public official and recently as a diplomat, Mrs Clinton has long showed a tendency toward bluntness, sometimes followed by a softening of her comments.
But her remarks about Pakistan's lack of action against al Qaida comes at a particularly sensitive moment - amid a major Pakistani offensive against militants and a deadly spate of insurgent violence.
Mrs Clinton was wrapping up her three-day visit to Pakistan today with a series of interviews with Pakistani journalists - including a session with women journalists that was to be broadcast live - and talks with leaders of parliament.
She will then fly to the Persian Gulf city of Abu Dhabi for meetings with Palestinian president Mahmoud Abbas, to be followed over the weekend by a meeting in Israel with prime minister Benjamin Netanyahu.
With Pakistan reeling from Wednesday's devastating bombing that killed more than 100 people in Peshawar, Mrs Clinton also engaged in an intense give-and-take with students at the Government College of Lahore. She insisted that inaction by the government would have ceded ground to terrorists.
"If you want to see your territory shrink, that's your choice," she said, adding that she believed it would be a bad choice.
Richard Holbrooke, the special US representative on Afghanistan and Pakistan, said Mrs Clinton was meeting the army chief, General Ashfaq Parvez Kayani, for an update on the offensive that began on October 17 against Taliban forces in a portion of the tribal areas near the Afghan border.
During her exchange with the Pakistani journalists, one reporter asked Mrs Clinton why the fight against terrorism seemed to put Pakistan at the centre and why other countries could not do more.
Mrs Clinton noted that al Qaida had launched attacks on Indonesia, the Philippines and many other countries over the years.
"So the world has an interest in seeing the capture and killing of the people who are the masterminds of this terrorist syndicate. As far as we know, they are in Pakistan," she said.
On Mrs Clinton's flight to Islamabad after the interview, US ambassador Anne Patterson said Mrs Clinton's remarks reflected what the Obama administration had told Pakistani officials in private.
"We often say, 'Yes, there needs to be more focus on finding these leaders'," Ms Patterson said. "The other thing is, they lost control of much of this territory in recent years and that's why they're in South Waziristan right now."