Pakistani officials say they are using documents found with an alleged lieutenant of Osama Bin Laden to hunt down more suspects.
It is not certain if Bin Laden is alive
American officials are continuing to interrogate the man thought to be al-Qaeda's chief of operations, Khalid Sheikh Mohammed, who was arrested in Rawalpindi on Saturday.
His arrest has led to renewed speculation about Bin Laden's whereabouts.
One Western intelligence official told the BBC that there was a very high probability that Sheikh Mohammed and Bin Laden had met in recent weeks.
Investigators are tracing Sheikh Mohammed's movements which include a visit to Quetta in Balochistan.
They believe he kept in contact with Bin Laden through e-mails and hand-delivered messages and may have an idea where he is hiding.
The US - whose agents are now believed to be interrogating Sheikh Mohammed at Bagram air base in Afghanistan - hopes the capture could lead towards the al-Qaeda leader.
But Pakistani officials are playing down speculation that Bin Laden is in their country or could be caught soon.
The White House has denied rumours circulating in Washington that it is about to capture the al-Qaeda leader.
The arrest of Sheikh Mohammed - thought to be al-Qaeda's chief operations planner and the mastermind of the 11 September attacks - has been seen as an important blow against the terror network.
Correspondents say US officials were also pleased to capture Mustafa Ahmed al-Hawsawi - named as the financier of the attacks on New York and Washington - in the same raid.
The BBC's Islamic affairs analyst, Roger Hardy, says Pakistan is continuing to co-operate with the US intelligence agencies, although President Musharraf is likely to have mixed feelings.
While the capture of the two al-Qaeda suspects reinforces the claim that Islamabad is working with the US in its war on terror, our correspondent says it is embarrassing that so many alleged members of Bin Laden's team turn up on Pakistani soil.
He adds that there is a suspicion that Mr Musharraf is playing a double game - giving the appearance of full support to the US while trying not to provoke a backlash from sections of Pakistani society which sympathise with al-Qaeda.
Pakistan is playing down reports that the two men met last month
Officials in Islamabad have repeated that there is no real evidence to suggest Bin Laden is in Pakistan - even if he is still alive.
But they confirmed that action was being taken on what they called incriminating evidence found at the house in Rawalpindi where Sheikh Mohammed was arrested.
The BBC's Zaffar Abbas in Islamabad says the documents include some undated letters handwritten in Arabic.
While some newspapers have reported it is Bin Laden's handwriting, our correspondent says a senior Pakistani official cautions that only US experts can make a positive verification.
Authorities in Pakistan also insist that Sheikh Mohammed did not reveal where Bin Laden was when questioned and they have cast doubt on speculation that the two met last month.
"That's pure conjecture and speculation. There is nothing in the material with us that would suggest that he met Bin Laden in Rawalpindi or anywhere in Pakistan in February," one interrogator said.
However, the documents do suggest that a number of prominent al-Qaeda members may still be hiding inside Pakistan.
Security agencies have stepped up the efforts to locate these men, some of whom are believed to be in the country's tribal region, close to the border with Afghanistan.