White House spokeswoman Dana Perino also said Washington was "encouraged" by talks between Ankara and Baghdad about efforts to "beat back" extremists from the Kurdistan Workers' Party (PKK).

"We also continue to watch the situation in northern Iraq. As we have said before, the PKK is a common enemy. We have been strongly supporting Turkey in its efforts to combat the PKK," she told reporters.

"We have encouraged dialogue and coordination between the United States, Turkey and Iraq, but we have not and we will not negotiate or hold talks with the PKK, nor do we expect Turkey to do so," she said.

The PKK, listed as a terrorist group by Ankara and much of the international community, has been fighting for self-rule in Kurdish-majority southeastern Turkey since 1984 in a conflict that has claimed more than 37,000 lives.

Ankara estimates that there are some 4,000 PKK rebels taking refuge in Iraq's northern Kurdish area, where there has been an autonomous regional government since the early 1990s.

Perino's comments came after the former number two US commander in Iraq, Lieutenant General Raymond Odierno, had warned that "that the long-term solution in northern Iraq is not a military one" and appeared to promote talks between Turkey and the PKK.

"Obviously, there's pressures that have to be put on them so we can start to talk and have negotiations with these terrorist elements," Odierno told reporters at a briefing on Tuesday.

Asked about those comments one day later, US Defense Secretary Robert Gates replied: "I don't think that anybody, certainly nobody I talked to, was of a mind to have any conversations with the PKK.

"I think that the real objective is to peel away, from the hardcore terrorists, those who might be reconciled and brought back into the political fold," he told reporters.

Gates cited the importance of Turkey making "efforts to try and address some of the civilian concerns among the Kurdish population where they recruit people, where the PKK recruits people."