"We've also made it clear to the Turkish government that anything that could lead to escalated concerns or civilian casualties; we have concerns about those steps," White House spokesman Scott Stanzel told reporters aboard Air Force One.

The comment came amid new attacks early Wednesday by Turkish bombers on positions inside Iraq of the Kurdistan Workers' Party (PKK), the third round of such strikes in ten days confirmed by Ankara.

But Stanzel reiterated that the United States regards the PKK, which groups Kurds battling the Turkish government, partly from bases inside Iraq, as terrorists.

"The PKK is a terrorist organization," Stanzel said. "The Iraqis don't want terrorists in their country and the PKK is a destabilizing force in the northern part of Iraq. So we continue to work collaboratively, both with Iraq and Turkey, on these issues."