"We are concerned about the continuing skirmishes that are happening up there, and terrorist attacks that are being launched by the PKK (Kurdistan Workers' Party) against the Turks," said spokeswoman Dana Perino.

"We continue to urge both sides to exercise restraint -- meaning the Iraqis and the Turks -- in terms of escalating tensions between the two countries," she told reporters.

Turkish warplanes Wednesday bombed Kurdish rebel targets along the Iraqi border in southeast Turkey, the country's semi-official Anatolia news agency reported.

Fighter jets from an air force base at Diyarbakir, the main city in the mainly Kurdish southeast, bombed and destroyed several Kurdistan Workers' Party (PKK) positions, the agency reported.

The bombing targeted PKK routes particularly in high mountainous areas, it said.

Asked whether Washington viewed Turkish air strikes along the Turkey-Iraq border as an escalation of the conflict, Perino replied: "I have not heard it characterized it that way."

And US Secretary of State Condoleezza Rice said Washington hoped both sides would find a way to defuse the tensions.

"We have encouraged several things: one is that the Iraqis and the Turks should make extraordinary efforts (together)," she told Congress.

Rice welcomed the Iraqi government's announcement that is closing down PKK offices and acting to prevent the cross-border movement of rebel fighters.

"It's very difficult because these people are in very remote areas of Iraqi Kurdistan, but that is not an excuse," she told the House of Representatives Foreign Relations Committee.