The semi-official Anatolia news agency said Turkish warplanes bombed several Kurdish Workers Party (PKK) positions in provinces along the border with Iraq, and that helicopter gunships also took part in raids.

"I don't know that there have been any Turkish air strikes or cross border operations into Iraq," said Major General Richard Sherlock of the US Joint Staff.

A Pentagon official, who spoke on condition of anonymity, said there had been no reports in US military channels of Turkish air strikes on either side of the border.

Separately, a senior US defense official told reporters that there was increasing sympathy in Washington for Turkey's insistence that "concrete and tangible" actions be taken against the PKK.

"I don't want to get into too much detail. But there are logistics lines, there are things we've done to curtail movement of the PKK."

"There are a variety of things that might be done to make it if not impossible, much more difficult for the PKK to operate across the border, which would also be visible to the government of Turkey," he said.

The US side is pressing for a diplomatic solution to the crisis but the senior official acknowledged that the Turks are under "volatile" domestic political pressure and may be forced to act.

"I would say within the senior reaches of the US government there is increasing sympathy for the Turkish position that something has to be done," the official said.

He said it was the responsibility of both the Iraqi government and the Kurdish regional government to take measures to stabilize the situation.

"I don't think we're going to be prescriptive about who does what, but I think we expect some tangible, concrete things to happen," the official said.

He added that the threat of Turkish military action had "concentrated people's minds" in Baghdad and in the Kurdish regional government.

"So I think we've perhaps the best chance to get some things done in quite some time," he said.