But the Northern Alliance has a credibility problem, for both political and military reasons

In the short run, the American aim seems to be to pile the pressure on the Taleban without, as yet, making their removal from power an explicit goal.

This is designed to achieve several things:

• To rattle the Taleban psychologically
• To encourage defections in Taleban ranks,
• To give the Taleban one last chance to surrender the Saudi-born radical Islamist Osama Bin Laden

It has to be said that it seems unlikely that the Taleban will hand Bin Laden over.

But beyond these short-term aims, US officials are clearly looking ahead to what a post-Taleban Afghanistan might look like.

The US increases political and military pressure on Taleban supporters

They are considering how best they can help the coalition of anti-Taleban forces known as the Northern Alliance.

They are also encouraging the Alliance's main regional allies, Russia and Iran, to do more.

But the Northern Alliance has a credibility problem, for both political and military reasons.

Its leaders believe they have a unique chance to get US backing in a new drive to topple the Taleban.

But before committing themselves, US officials are understandably being cautious.

Ethnic questions

The Alliance lacks support from the country's dominant ethnic group, the Pashtuns.

There is much speculation about a role for the ex-king Zahir Shah - he is a Pashtun - but he is 86 and has no military faction at his command.

On the ground much of Afghanistan is under the control of local Pashtun warlords - military commanders some of whom have no inherent loyalty to the Taleban, and may well switch sides if they think the Taleban are about to be swept from power.

Finally, the Americans cannot afford to exclude Pakistan from any decision-making about Afghanistan's future.

The Pakistanis have little choice but to accept the demise of their prot�g�, the Taleban.

But they will insist on maintaining a future role in a country they regard as within their sphere of influence.