The assistant secretary of state for Europe, Dan Fried, made the appeal in a telephone call to Turkish Ambassador Nabi Sensoy after Turkey's army chief argued publicly in favor of a military incursion into northern Iraq to crack down on Kurd rebels there, US officials said.

State Department spokesman Sean McCormack said Fried told the envoy such incursions were "an option that everybody should work to avoid."

Fried urged the Turkish government to pursue US-brokered negotiations with leaders of the Kurdish autonomous area of northern Iraq aimed at curbing the activities of the separatist Kurdistan Workers' Party, or PKK, which Washington and Ankara consider a terrorist group.

"The focus should be on trying to resolve this in a cooperative way, in a joint way, rather than to resort to unilateral actions," McCormack said.

But the US spokesman went on to say it was imperative to counter the PKK, which has waged a bloody campaign for Kurdish self-rule in Turkey's southeast since 1984, an insurgency that has already claimed about 37,000 lives.

"Clearly the terrorist activities of the PKK are completely unacceptable," he said. "They are a terrorist group and they need to be dealt with."

The US reacted after Turkey's top military commander, General Yasar Buyukanit, told a press conference: "If you ask me whether a cross-border operation is needed, yes it is needed. It would be useful."

The army, he said however, had not yet asked the government for parliamentary authorization for an incursion into Iraq.

A special US envoy, retired general Joseph Ralston, has been trying for months to lower tensions between Turkey, a key US military ally, and Iraqi Kurdish leaders whose support is essential for US efforts to stabilize that country.

But the dispute has only worsened in recent weeks, when there has also been an upsurge of fighting in Turkey between the army and PKK units, which have left 10 soldiers and 29 rebels dead this month.

Ankara fears that moves towards Kurdish independence in northern Iraq could fuel the PKK's separatist campaign in southeast Turkey.

Washington for its part is concerned that Turkey operations against PKK bases inside northern Iraq could destabilize one of the few relatively stable parts of the country.