For many people in the West, Iran and the Taleban represent two equally unacceptable faces of Islamic militancy.

Faced with the prospect of war breaking out between them, the man in the street might well shrug his shoulders.

But for Western policy-makers, the dispute between Tehran and Kabul is complicated and dangerous - and adds another unwelcome crisis to the international agenda at a time of weakened Western leadership because of President Clinton's domestic predicament.

The Western powers regard Iran and the Taleban as troublesome - but believe they must engage with both, as players in a strategically sensitive region.

Ever since Afghanistan ceased being an arena of Cold War rivalry, the West's priority has been to see the emergence of a strong central authority there.

So far, in bringing most of Afghanistan under their control, the Taleban have managed to alienate the country's minorities and alarm their neighbours.

But realists in Western capitals argue that the Taleban are the dominant force in the country - and that the aim of Western policy should therefore be to moderate their behaviour rather than cold-shoulder them.

Similarly, Western powers - including, in a quiet shift of policy, the United States - would prefer a constructive relationship with the mullahs in Tehran.

As with the Taleban, they disapprove of particular actions by the Iranian government but want to encourage it to play a positive regional role.

'Full-scale invasion unlikely'

The current crisis is accordingly viewed as an important test of Iranian foreign policy.

Next week, Iran's President, Mohammed Khatami, is due to address the UN General Assembly in New York.

If the visit goes ahead, it would be another step in bringing Iran in from the cold.

If, on the other hand, the Iranians were to launch a full-scale invasion of Afghanistan, that would destroy any chance of a rapprochement with the West and seriously damage their international standing.

At the moment, a full-scale invasion looks unlikely.

While piling up the pressure on the Taleban, Iranian officials are continuing to press for international action, particularly by the UN. The Taleban want international recognition - and that may give the big powers a degree of leverage.