Related: U.S. Pledges to Work with Turkey, Iraq on PKK Rebels

The United States on Tuesday expressed opposition to Turkey's attempt to launch a unilateral incursion into Iraq in pursuit of separatist ethnic Kurds.

"I am not sure that unilateral incursions are the way to go, the way to resolve the issue," U.S. State Department spokesman Sean McCormack said of Turkey's latest warning that it would authorize an military operation inside Iraq against Kurdish rebels if it deemed necessary.

"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 told reporters.

Also on Tuesday, U.S. National Security Council spokesman Gordon Johndroe said that the United States would be working with Turkey and Iraq to combat the separatist Kurdistan Workers Party, or PKK, which has carried out a series of attacks in Turkey.

But he declined to say whether the White House would support Turkey authorizing a possible incursion into northern Iraq, where the PKK militants are believed hiding, calling that a hypothetical question.

In addition, White House spokeswoman Dana Perino also said that the Bush administration would be "committed to working with Turkey to deal with the terrorism problem, with the PKK in northern Iraq. "

Asked if Washington would support an incursion by Ankara, the spokeswoman said "I think it's premature."

Turkish President Abdullah Gul has vowed to take all necessary measures against Kurdish rebels, including a possible incursion into northern Iraq after a total of 13 Turkish soldiers were killed on Sunday.

The PKK, listed as a terrorist organization by Turkey, the United States and the European Union, launched an armed campaign for an ethnic homeland in the mainly Kurdish southeastern Turkey in 1984, sparking decades of strife that has claimed more than 30, 000 lives.