American forces hunting al-Qaeda fighters in Tora Bora believe they heard a radio transmission from Osama bin Laden earlier in the week, fueling US optimism that he is trapped in the mountain enclave in eastern Afghanistan, officials said.
The officials cautioned that they could not be sure whether bin Laden had escaped in the meantime, or even 100 per cent certain that it was his voice on the short-range radio. "It's pretty difficult to be sure that's who you're listening to," one defence official said.
But as US warplanes pounded mountain ridges in Tora Bora, officials in Washington and at the headquarters here of the US Central Command, which oversees the US military operations in Afghanistan, said they were increasingly confident that the climactic battle of the war was at hand.
Senior commanders said they had assumed early on that the war eventually would narrow to a single area, but they had not known where the battle would come and had underestimated the number of caves in the vicinity of Tora Bora.
"If not there, we thought this battle would have been some place," said Marine Lieut Gen Mike DeLong, deputy chief of Central Command. "We figured we would end up looking at the war through a soda straw."
The Tora Bora area, according to another senior Central Command officer, was always at the top of the Pentagon's list of potential hideouts for bin Laden, although the US military's knowledge of the area was incomplete.
"We started out thinking there were fewer than 100 caves," recalled Maj Gen Gene Renuart, CENTCOM's director of operations. "Many of them looked unused. In the first few days of airstrikes, we hit 10 or 12 that showed the greatest promise of being used."
In subsequent weeks, US war planners obtained a much more detailed view of the cave and tunnel network, in part by consulting with Russian and European mining companies as well as US firms that had worked in the area. CENTCOM's list of potential hideouts now numbers several hundred, many of which have been bombed over the past several weeks as the war has concentrated in the White Mountains south of Jalalabad.
"It's really been a detective process, working with any sources we could" Maj Gen Renuart said. "We don't even know whether we've found all the places yet."
One reason for their continuing belief that bin Laden is in the Tora Bora area, US commanders said, is the fierceness of the resistance by al-Qaeda forces there. They say bin Laden's largely non-Afghan force is hemmed into the Agam and Wazir valleys, with Afghan opposition troops and US and British commandos in front of them and towering, snow-covered peaks behind them.
But military intelligence assessments of bin Laden's whereabouts still carry qualifying remarks, citing conflicting reports suggesting the terrorist leader might have fled across the border into Pakistan.
To help in the search, US military officials have queried defence laboratories and private firms about the existence of any experimental devices capable of detecting humans behind tons of granite. No such technology has surfaced.
"Oil companies have devices that can see through rock looking for oil," DeLong said. "But we're not looking for oil. We've found very few new things of that sort to use in our search."
In contrast to the narrowing hunt for bin Laden, officials here say they have received little reliable information about the location of Taliban leader Mohammed Omar since the fall of Kandahar two weeks ago. Up to that point, US defence and intelligence officials appeared confident that the one-eyed fundamentalist cleric was in the Kandahar area.