British diplomats said operations would begin within a week.
Britain has more than 50 aircraft and 8500 personnel taking part in an exercise in Oman.
The US has sent more than 500 planes to the region as well as aircraft carriers and troops.
Military analysts say the first phase of the operation will involve suppressing Afghan air defences before an attempt to secure the Bagram Air Base north of Kabul.
Afghanistan's only all-weather airfield, it is the ideal jumping-off point for American and British special forces, even though they have no clear idea where bin Laden is.
The preparations are gaining urgency with the onset of winter.
Snow is already falling on the Khyber Pass and ground operations by special forces will be almost impossible within a few weeks.
Pressure is also growing in America for a decisive response to the September 11 attacks.
Prominent Republican commentator William Kristol has attacked Secretary of State Colin Powell for undermining President George W. Bush. He also warned Mr Bush that he could face trouble from the party if he steered too moderate a course.
But Defence Secretary Donald Rumsfeld cautioned against expectations of a major invasion of Afghanistan, saying the war against terrorism was "not about revenge".
Mullah Omar's confirmation that Afghanistan would not hand over bin Laden came in an interview banned from the airwaves by the US State Department but published in the Washington Post.
"If we did, it means we are not Muslims, that Islam is finished," he told the state-owned Voice of America radio network.
"This is not an issue of Osama bin Laden. It is an issue of Islam. Islam's prestige is at stake. So is Afghan tradition."
In a separate plea, Mullah Omar urged Americans to use "your own sense and understanding".
"Can Osama bin Laden carry out such an act in America?"
In a further sign of resistance, anti-US protesters in Kabul stormed the long-abandoned American embassy, setting fire to it.
The pending war is causing chaos in Afghanistan, with thousands fleeing their homes, others at risk of starvation, and insurrection in the north.
Fierce fighting was reported as the Taleban staged a counter-attack to block the Northern Alliance opposition's advance towards Mazar-i-Sharif, the major city on routes to the border with Uzbekistan.
In the western province of Badghis, the Taleban recaptured Qadis district after losing it briefly to opposition forces on Tuesday.
The UN High Commissioner for Refugees urged Pakistan and Iran to open their borders to refugees.
Many Afghans have abandoned the southern city of Kandahar, the seat of Taleban power.
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America
