"I am not sure that unilateral incursions are the way to go, the way to resolve the issue," said State Department spokesman Sean McCormack.

"We have counseled them both in public and private for many, many months (on) the idea that it is important to work cooperatively to resolve this issue," McCormack added.

At the White House, spokesman Dana Perino, said any incursion by Ankara was "a hypothetical right now."

"We have long been supportive of Turkey, to make sure that they have what they need in order to stop terrorist activity in northern Iraq. The Iraqi government is in agreement with that as well," she said.

Turkey earlier Tuesday threatened a military incursion in northern Iraq as part of stepped up measures against Kurdish rebel bases in the region.

The government said in a statement that it had given orders allowing for all legal, economic and political measures, "including a cross-border operation if necessary," against a "terrorist organization in a neighboring country."

The statement was taken to refer implicitly to the outlawed Kurdistan Workers' Party (PKK) and Iraq.

Perino said the US administration was "focused on cooperating with the Turks and the Iraqis to make sure that the PKK can be stopped, that the violence that threatens not only Turkey, but Iraqis as well, can be curtailed right there in northern Iraq, and the Iraqi government is committed to working hand in hand with the Turks on that."

Earlier, Prime Minister Recep Tayyip Erdogan had met senior government and military officials to discuss tougher action against the PKK -- listed as a terrorist group by Ankara and much of the international community -- after the rebels killed 15 soldiers in weekend attacks.

Ankara says the PKK enjoys free movement in northern Iraq and obtains weapons and explosives there for attacks across the border.

It has also accused Iraqi Kurds of tolerating and even supporting the rebels.