The US has been dropping cards offering a reward
According to US intelligence sources, Bin Laden's voice was detected last week at the Tora Bora cave complex, which is reportedly now under opposition control.
A senior al-Qaeda leader Abu Jaffar told the British Daily Telegraph newspaper that Bin Laden had crossed the border with the help of Pashtun tribesmen.
Dozens of al-Qaeda fighters have reportedly crossed via mountain passes in the country in recent days, and some analysts suggest Bin Laden could be among them.
Crackdown
Pakistani authorities, who have sent 4,000 troops to the region backed up with helicopter gunships, say they have arrested 30 al-Qaeda suspects.
The rugged frontier is difficult to police, and is an autonomous zone within Pakistan.
Security matters are usually left to the local tribes, many of who are sympathetic to al-Qaeda.
A BBC regional analyst says Bin Laden could be on the move in the area with a small group of hardened fighters who are unquestioningly loyal to him.
Other options for Bin Laden could include the central Asian republics of Uzbekistan, Kyrgyztan and Tajikistan.
The Agence France Presse agency speculates that Islamic Movement of Uzbekistan militants, who are believed to operate secret routes from Afghanistan to the Ferghana valley, may be sheltering Bin Laden.
All three countries were targeted by Islamic militants last year in a wave of attacks aimed at destabilising the region, allegedly backed by al-Qaeda and the Taleban.
Some analysts have suggested Iraq as a possible destination for Bin Laden, based on allegations that one of his closest aides led a scouting party to Iraq three years ago to inspect possible sites for future bases.
But Baghdad has strongly rejected claims of ties to al-Qaeda, and has publicly distanced itself from Bin Laden.
Sudan, where Bin Laden was based before Afghanistan, and Yemen, where al-Qaeda also reportedly has bases have also been suggested as possible hide-outs.
Somalia and Chechnya, both countries where sympathetic Islamic militant groups are believed to operate, could also offer Bin Laden sanctuary.
Death rumours
However, last week Pakistan's al-Akhbar newspaper reported that Bin Laden and Taleban leader Mullah Mohammed Omar were shot by their own consent in Kandahar the day the city fell to anti-Taleban forces.
This unconfirmed story was brought to Karachi by Afghan families fleeing to Pakistan, the newspaper said.
The BBC regional analyst also says that Bin Laden probably has no intention of being taken alive and put on trial.
"He seems ready to die, in the firm belief that after him will come other Bin Ladens to continue the struggle," he said.