The United States has given Turkey too much encouragement for its incursion into northern Iraq, if only by sending ambiguous signals that - late in the day - it has tried to clarify. The result is that Turkey is showing no signs of leaving the territory, at a particularly fragile point in Iraq's own politics.

This week, in remarks that were a curious combination of casualness and precision, Robert Gates, the Defence Secretary, said that it would be a good idea if the Turkish military stopped its pursuit of militants in northern Iraq by mid-March.

His words were interpreted as a clear change from earlier American statements that had seemed to endorse Turkish action against the Kurdistan Workers' Party, or PKK. “It's very important that the Turks make this operation as short as possible and then leave”, he said. “I measure quick in terms of days, a week or two, something like that, not months.”

It is odd that he can so precisely time the demands of a campaign against PKK fighters that has preoccupied Turkey for more than two decades, and which feeds off the unresolved status of northern Iraq within its own country.

That sharp range of mountains along Turkey's southern border is one of the few geographical features that makes the country seem like part of Europe. If you fly from Baghdad to the US air base in Incirlik, just over the Turkish border, the peaks rear up as an abrupt wall between the sand-coloured hills of northern Iraq, and Turkey's surprising greenness.

It is not territory that makes for a quick fight. There is no denying that PKK fighters are exceptionally unpleasant, and that Turkey is justified in wanting to do something about this provocation, and indeed, in resisting the calls for a "Kurdistan” spanning the border.

The US has always backed short incursions in direct pursuit of PKK militants. But for the US to endorse cross-border action by thousands of troops for more than a month is to tolerate the injection of a hugely disruptive new element. Turkish officials have reacted to these mixed, but warm, signals by showing absolutely no urgency in leaving.

The relaxed American attitude to the introduction of more provocation into Iraq is the more surprising because this has been a discouraging week, after months of falling death figures. The surprise has been the rejection by Iraq's presidency council of a crucial election law passed by parliament.

The provincial powers law was one of several important pieces of legislation designed to reconcile the three main ethnic groups of Iraq, and the competing claims of different provinces.

It would have paved the way for provincial elections in the autumn, allowing Sunnis, who largely boycotted the polls three years ago, to regain some ground. Without progress on this front, the gains from the American “surge” of forces, and from the success in winning support from previously hostile Sunni groups, could fade quickly.

America's reflex in defending Turkey, a crucial Nato ally, is better than its indifference. But this was not the moment to give a blessing to so inflammatory a move.

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