The United States has opened a "diplomatic full court press" to urge Turkey not to invade northern Iraq, the State Department said Monday, as tensions between the two countries soared following an ambush by rebel Kurds that killed 12 Turkish soldiers and left eight missing.

Secretary of State Condoleezza Rice called Turkish Prime Minister Recep Tayyip Erdogan and the leader of Iraq's Kurdish region, Massoud Barzani, on Sunday to press the U.S. case for restraint from Turkey and Iraqi action against the outlawed Kurdistan Workers' Party (PKK), department spokesman Sean McCormack said.

"We do not believe unilateral cross-border operations are the best way to address this issue," he said, describing Rice's call to Erdogan, whose government has threatened military incursions into Iraq to deal with the PKK. "It's important that there be action to counter the PKK."

"In our view, there are better ways to deal with this issue," he said, stressing that United States regards the PKK as a terrorist organization. "We think the best way to do this — and that is to address the PKK threat — is for the Turks and the Iraqis to work together to mitigate it and eliminate it," McCormack added.

"We are going to do everything we can to encourage Turkey and Iraq to work together to address what is a common threat," he told reporters, adding that Washington wants authorities in Iraq to step up their efforts against the PKK.

"She (Rice) underlined to President Barzani the importance of Iraq working actively with the Turkish government to counter what is a real threat to Turkish citizens," he said. "It's important that there be action to counter the PKK."

Erdogan said earlier that he had told Rice that Turkey expected "speedy steps from the U.S." in cracking down on Kurdish rebels and that Rice had asked "for a few days" from him.

McCormack did not dispute the account of the conversation but declined to comment on what Rice had meant by asking for "a few days."

As Rice was speaking to Erdogan and Barzani, McCormack said, the U.S. Ambassador to Iraq, Ryan Crocker, was making similar points in Baghdad with Iraqi President Jalal Talabani — himself a Kurd — who ordered the PKK to lay down their arms or leave Iraq, and Iraqi Prime Minister Nouri al-Maliki.

The spokesman added that he "would not be surprised" if White House officials, including possibly President Bush, followed up the Rice and Crocker conversations with Turkish and Iraqi officials.

"From our perspective this is a diplomatic full-court press," McCormack said. "We want to see an outcome where you have the Turks and the Iraqis working together and we will do what we can to resolve the issue without a Turkish cross-border incursion."

Meanwhile in Turkey, dozens of Turkish military vehicles loaded with soldiers and heavy weapons rumbled toward the Iraq border. An AP Television News cameraman saw a convoy of 50 military vehicles, loaded with soldiers and weapons, heading from the southeastern town of Sirnak toward Uludere, closer to the border with Iraq.

It was unclear whether the vehicles were being sent to reinforce troops engaged in fighting with rebels on Turkish soil or were preparing for possible cross-border action. Tens of thousands of Turkish troops are already deployed in the border area.

At the same time, Turkish Foreign Minister Ali Babacan said his country will pursue diplomacy before it sends troops across the rugged frontier.

"We will continue these diplomatic efforts with all good intentions to solve this problem caused by a terrorist organization," Babacan told reporters in Kuwait where he was visiting as part of a tour of Arab states to explain Ankara's plans. "But in the end, if we do not reach any results, there are other means we might have to use."

Sunday's ambush outraged an already frustrated Turkish public and demonstrations erupted across the country while opposition leaders called for an immediate strike against rebel bases in Iraq, despite appeals for restraint from Iraq, the U.S. and European leaders.

The Turkish military confirmed Monday that eight of its soldiers were missing after the PKK ambush that left 12 other soldiers dead and brought the northern Iraq border area to the brink of war. The military said its counteroffensive left 34 rebels dead.

The pro-Kurdish Firat news agency, based in Belgium, released the names of seven people it said were Turkish soldiers captured by separatist fighters in Sunday's ambush. It said an eighth soldier was also taken captive but did not release his name.

Turkey's military said Sunday it had launched an offensive backed by helicopter gunships in retaliation for the attack, shelling rebel positions along the rugged Turkish-Iraqi border.

The rebel attack occurred four days after the Turkish Parliament authorized the government to deploy troops across the border in Iraq, amid growing anger in Turkey at perceived U.S. and Iraqi failure to live up to pledges to crack down on the PKK.