Yesterday’s anti-US demonstration in the Afghan capital Kabul in protest against Monday’s bombing mistake in which some 40 civilians, among them 25 wedding guests, were killed is a serious development. It is the first time since the fall of the Taleban regime that Afghans have protested against the US whose forces, which, most of them have till now regarded as liberators. It may be a taste of things to come.

The Afghans have been historically suspicious of foreigners, even those who came to their aid. Similarly, they close ranks when any of their own are seen to be under attack by outsiders, even if in other circumstances those suffering are long-standing political or tribal enemies. That will account for some of the animosity toward the US, unleashed by the bombing blunder. Tempers, however, cannot have been improved by the Pentagon’s bullish defense of what happened. Claims that its planes were attacked first by anti-aircraft fire when there is tangible evidence of dead wedding guests only serve to inspire distrust. It may be that the pilot mistook celebratory bullets for anti-aircraft fire but whatever the cause, it would have been better if the Pentagon had exercised some diplomatic discretion rather than engaging in vigorous justification. Clearly, the Pentagon has still not learned the lesson from other instances of “friendly fire” — in Bosnia, Kosovo and one earlier occasion in Afghanistan — that it is better to express regret and an intention to discover the truth than go in for bullish justifications that subsequently turns out to be wrong.

Afghanistan needs as few excuses for trouble making as it can get: it is not just in the Afghans’ interests that events there should remain as calm and sweet as possible, it is also in Washington’s. There are still deep divisions, and there is a long way to go before the pain and anger of the past 30 years can be assuaged. As the UN reported only a couple of days ago, there remain thousands Afghans refugees stuck on the Pakistan border some of whom are not, as might be imagined, trying to get back home, but into Pakistan, afraid for their lives as northern Pashtuns and accused of being Taleban supporters. And a few days before, in another sign of potential instability, continuing friction between rival northern warlords forced the UN to suspend its program of returning refugees to the region.

Besides, there are certainly elements in the country who hate those who overthrew the regime. They will use any opportunity to turn people against the new government and its friends, especially Americans. The US cannot afford to blunder into unpopularity in Afghanistan. The Afghans, many of whom have already put the Taleban regime behind them and think now only about the future, would forget why the US is there and begin to regard it as yet another foreign occupier if there were more blunders. That would put everything that it has done there at risk, including the popularity of the Karzai government. Washington can comfort itself with the fact that it was a small demonstration, just some 200 protesters. But it must take it as a warning. US troops have to think, and think again, before they act. There is too much at stake. Washington cannot allow its alliances and political interests to be undone by the practice of shoot first, ask questions afterward.