The most intense ground assault of the war began yesterday. Northern Alliance forces advanced on the Tora Bora region, the network of caves and tunnels where Osama bin Laden is believed to be hiding. Supported by US aircraft, tanks and special forces, the tribal fighters reportedly seized a ridge in the area and met resistance from 1,000 al-Qaeda fighters loyal to bin Laden.
After the initial bombing, the al-Qaeda fighters surfaced from their caves and fired mortars at Northern Alliance soldiers who tried to move their ageing Soviet-built T-55 tanks forward.
Hours later, hundreds of Northern Alliance fighters in small groups launched a three-pronged attack and climbed narrow mountain trails under the cover of tank fire.
The day of heavy conflict began just after dawn, when B-52s and other F-18 fighter jets pounded Tora Bora deep in the White Mountains near the eastern city of Jalalabad.
The relentless nature of the air campaign was apparent even in Kabul, some three hours drive from Tora Bora, as F-18 fighters jets roared through the skies during much of the night and throughout the day.
After unusually heavy B-52 carpet bombing on Sunday, the Pentagon said it had dropped a 15,000lb "daisy cutter" bomb on the entrance of a cave in which US forces thought al-Qaeda senior leadership, possibly including Osama bin Laden, may have been hiding.
A spokesman, Rear Admiral John Stufflebeem, said the huge bomb, the third of its kind to be dropped in the course of the campaign, was intended to kill those inside and render the cave unusable in the future.
He said the cave had been targeted because "it was believed that that's where some substantial al-Qaeda forces would be, and possibly including senior leadership". He added that it had been impossible to check how many casualties there had been in the blast.
In the south, Marine convoys and helicopters left their Camp Rhino in the desert south-west of Kandahar to reinforce patrols that had fanned out across the area in recent days to hunt for fleeing Taliban.
And in a sign widely interpreted here as an indication of US confidence that the Taliban have been thoroughly routed, Marines swept into the former American embassy in Kabul, occupying it for the first time in 12 years.
It was a preliminary step towards the eventual re-establishment of a US diplomatic presence - and marked the first known US military presence in the Afghan capital since it fell to the alliance.
An explosives team swept the grounds and a State Department assessment team went to work inside, guarded by the Marines, a military spokesman said.
Army major Victor Harris, speaking to reporters here, said no timetable had been set for any reopening. It had not even been decided whether the United States would keep this site or find a new one. Maj Harris said the army presence in Kabul was an embassy security detail, working under the auspices of the State Department, and should not be regarded as a combat contingent.
The embassy compound was attacked on September 26th by a mob, which set the guardhouse ablaze and tore down the large metal US seal at the entrance, while Taliban police looked on. Other countries are also beginning to resume a diplomatic presence. Plans for a new Afghan government continue to move ahead. Mr Lakhdar Brahimi, the UN special envoy to Afghanistan, will arrive in Kabul today to meet several signatories to the Bonn agreement. Mr Brahimi is also expected to discuss the growing food crisis in several parts of this country.