Mr Karzai cannot afford to drop his guard

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The interim leader of Afghanistan, Hamid Karzai, sets off today for the United States, where he will be guest of honour at President Bush's State of the Union address. He is assured a rapturous welcome, and his visit will doubtless temper American frustration that the central objective – of capturing Osama bin Laden "dead or alive" – has not been achieved.

That Mr Karzai, sworn in on 22 December, feels secure enough to travel outside Afghanistan is evidence that the situation in the country is becoming more stable. And, as his appeal at this week's Tokyo aid conference showed, he is a persuasive advocate of his country's cause. The time he spends outside his country is not wasted.

Nor has there been any slouching at home. In Kabul yesterday, Mr Karzai announced that the latest stage in the 18-month timetable towards constitutional government had been completed on time. The panel was named to organise a tribal assembly this spring. Preparations for the assembly will give many Afghans the first chance to make their voices heard for almost two decades. So far, then, so much better than expected.

Yet there are warning rumbles that need to be heeded. Skirmishes are taking place in the south between units associated with the interim government, backed by US special forces, and the residue of the Taliban and al-Qa'ida. In the north, fighting has been reported between troops of the two senior defence officials in Mr Karzai's government (and erstwhile rivals). And detachments loyal to Mr Karzai have their sights set on a powerful warlord in the west, who may have help from Iran.

Any Iranian intervention, overt or covert, should be discouraged by international pressure. But the allies could usefully ponder whether they have done enough to recognise Tehran's moral support for the US after 11 September, and its political cost to Iran's leaders.

Mr Karzai, meanwhile, should beware lest the adulation he receives in the US jeopardise his standing at home. No one, least of all Mr Karzai, can afford to drop his guard.