Nearly four years after the 11 September attacks, there are signs that the US is beginning to grow impatient at the lack of progress in the hunt for Osama Bin Laden - and particularly over the sensitive issue of Pakistan's co-operation in the search for the al-Qaeda leader.
Bin Laden has not been seen in public since 9/11
Last week the outgoing US ambassador to Kabul, Zalmay Khalilzad, said he believed that neither Taleban leader Mullah Omar nor Bin Laden were in Afghanistan.
Although he was careful not to say
explicitly that he thought they were in Pakistan, he came as close to saying it as is possible without offending diplomatic sensibilities.
In a later interview with an Afghan TV station Mr Khalilzad asked how it was possible for a Pakistani TV crew to find and interview a top Taleban commander when the Pakistani intelligence services did not know where he was.
Pakistan reacted angrily to the suggestion it was not doing enough and called Mr Khalilzad "irresponsible".
Now in an interview with Time magazine, CIA director Porter Goss has added to the debate.
He said he has "an excellent idea" of where Bin Laden is, but that "weak links" in the war on terror and "sanctuaries in sovereign states" were hampering the hunt.
Mr Goss's carefully worded comments again avoid naming any countries, but could also be interpreted as a suggestion that dealing with Pakistan over Osama Bin Laden has become a sensitive issue for the US.
One man who has seen that relationship from the inside is former CIA officer Gary Schroen.
He led the hunt for Bin Laden between 1997 and 1999 and then again after the attacks on 11 September.
In a BBC interview Mr Schroen recalls how the CIA's counter-terrorism chief told him one of his jobs was "to find Bin Laden and his lieutenants, kill them and bring back Bin Laden's head to the United States in a cardboard box on dry ice".
Mr Schroen believes the real opportunity to capture Bin Laden came in December 2001 at the Tora Bora caves in eastern Afghanistan.
"Once Bin Laden slipped over the border into Pakistan... he was effectively out of our reach because the Pakistani government has taken such a strong position that US military personnel will not enter Pakistan," he told the BBC.
"We really had to come back to depend on the Pakistanis."
Mr Schroen, who served with the CIA in Islamabad on two separate occasions, says that he is disappointed but not surprised the al-Qaeda leader hasn't been caught yet.
"The Pakistani government still is very reluctant to actually try to deal with Bin Laden because the uproar in their country will be tremendous if they are actually seen as facilitating his capture or his death."
Mr Schroen also argues that Pakistan does have a general idea of where Bin Laden might be: "I think they know as well as I do that if he's hiding anywhere in the country he's hiding north of Peshawar in the tribal areas along the border."
He acknowledges that the Pakistani government faces a tough battle if it sends troops into those areas but that if they were willing to conduct aggressive military operations, it would probably force Bin Laden to move and once that happens it would become easier to find him.
"But it all comes down to the big if - will Pakistan step up to this task?"
Anger in Islamabad
US relations with Pakistan over counter-terrorism have also been frayed by the arrest of a number of Pakistani men in California. Interrogators say one of the men confessed to training in an al-Qaeda camp inside Pakistan.
Pakistan has sent troops into its unruly tribal areas
In 2002, Pakistan banned a number of militant groups which had been involved in Kashmir, with the support of Pakistan's military, but which also had links to al-Qaeda.
Experts fear that these groups have simply moved underground and the arrests have raised concerns that they could be directing activities against the US.
Publicly, the US has always been careful to praise Pakistan's co-operation and acknowledge the risks it has taken and the lives it has lost in hunting al-Qaeda with more than 700 arrests.
President Musharraf has also been personally targeted for assassination by militants and so the suggestion that the country is not doing enough is one that generates serious anger in Islamabad and there's no doubt that President Musharraf has taken great political and personal risks in allying with the United States.
So far, there are only hints that the US may be beginning to lose patience with its ally's contribution but if those hints become anything stronger, there could be stormy times ahead in the most critical of relationships in America's war on terror.