SIRNAK, Turkey — Dozens of Turkish military vehicles loaded with soldiers and heavy weapons rumbled toward the Iraq border today after an ambush by guerrilla Kurds that left eight soldiers missing and killed 12.

Iraq’s president said the rebels would announce a cease-fire later in the day. Turkey’s government, which has rejected similar announcements in the past, said the country will pursue diplomacy before it sends troops across the rugged frontier.

Turkey’s military said it lost contact with the eight soldiers after yesterday’s clash and said 34 guerrillas had been killed so far in a counteroffensive. A pro-Kurdish news agency said the eight were captured — a claim that would make it the largest seizure since 1995, when guerrillas grabbed eight soldiers and took them to northern Iraq.

The ambush yesterday outraged an already frustrated public. Demonstrations erupted across the country and opposition leaders called for an immediate strike against rebel bases in Iraq, despite appeals for restraint from Iraq, America, and European leaders.

In Washington, the State Department said America has opened a diplomatic “full court press” to urge Turkey not to invade northern Iraq.

“In our view, there are better ways to deal with this issue,” a spokesman, Sean McCormack, said, stressing that America regards the Kurdistan Workers’ Party, known by its Kurdish acronym PKK, as a terrorist organization.

President Jalal Talabani, a Kurd, said the PKK would make a cease-fire announcement later today.

Turkey has rejected several past unilateral cease-fires declared by rebels, saying it would maintain fighting until all rebels surrender or are killed. In the past, rebels have pressed ahead with attacks despite cease-fires on grounds that they were defending themselves.

Mr. Talabani made the remarks to reporters at the airport in the Kurdish city of Sulaimaniyah before flying to Baghdad; his office confirmed them. More details were not immediately available.

Prime Minister Erdogan said he told Secretary of State Rice in a telephone conversation last night that Turkey expected “speedy steps from the U.S.” in cracking down on Kurdish rebels and that Ms. Rice, who called the Turkish leader, asked “for a few days” from him.

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

Mr. Erdogan did not specify what he meant by “speedy steps,” but he has often urged America and Iraq to crack down on the PKK. Turkish leaders say it is the responsibility of those countries to do whatever is necessary to destroy the guerrilla group’s bases in northern Iraq.

“We will continue these diplomatic efforts with all good intentions to solve this problem caused by a terrorist organization,” Foreign Minister Ali Babacan told reporters in Kuwait. “But in the end, if we do not reach any results, there are other means we might have to use.”

Mr. Babacan has been touring Arab countries to explain his country’s plans.

The Turkish military confirmed today that eight of its soldiers were missing after the ambush by Kurdish rebels that left 12 other soldiers dead and brought the northern Iraq border area to the brink of war.

“Despite all search efforts, no contact has been established with eight missing personnel since shortly after the armed attack on the military unit,” the military said in a statement on its Web site.

The pro-Kurdish Firat news agency, based in Belgium, released the names of eight people it said were Turkish soldiers captured by separatist fighters in yesterday’s ambush.

The last major kidnapping was in 1995, when Kurdish guerrillas grabbed eight soldiers and took them to bases in northern Iraq, where the group is still headquartered. The rebels released the soldiers two years later after human rights activists, lawmakers, and family members visited the rebel hide-out.

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.

More than 2,000 protesters in Istanbul, mostly members of an opposition party, denounced the attack by the PKK and urged the government of Mr. Erdogan to resign, the private Dogan news agency reported.

In Ankara, hundreds convened at a main square shouting “Down with the PKK and USA!” Ambulances decorated with Turkish flags drove around main streets, their sirens wailing.

Some 13,000 schoolchildren in Bilecik in eastern Turkey held a minute of silence while people marched down a main street, waving the Turkish flag, the state-run Anatolia news agency reported.

In Bursa, in northwest Turkey, some protesters walked to a military conscription office and asked to enlist to fight rebels.

Turkey’s military said yesterday 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 Parliament authorized the government to deploy troops across the border in Iraq, amid growing anger in Turkey at perceived American and Iraqi failure to live up to pledges to crack down on the PKK.

Yesterday’s attack raised the death toll of soldiers in PKK attacks in the past two weeks to around 30.