"Despite all searches, contact has not been established with eight staff with whom contact was lost," the Turkish army general staff said in a statement.

The Kurdistan Workers' Party (PKK) said it had captured the army personnel after it ambushed a military unit near the Iraqi border on Sunday, killing 12 soldiers.

The ambush triggered street protests in Turkey, as well as media and opposition calls for Prime Minister Recep Tayyip Erdogan to order an immediate military incursion against PKK bases across the Iraqi border.

The United States has urged Erdogan to hold off on military action, but the prospect of Turkish soldiers being held captive is sure to turn up the heat on the government.

The PKK, which has been fighting for self-rule in Turkey's mainly Kurdish southeast since 1984, named seven of the captured soldiers on the web site of a news agency linked to the group.

It said the identity of the eighth soldier would be revealed later.

Turks took to the streets for the second day running Monday, with some 3,000 flag-waving demonstrators in Istanbul shouting anti-PKK slogans and criticising Erdogan for hesitating over a military strike.

Last week, parliament authorized the government to send troops across the Iraqi border at any time it sees fit, amid Turkish anger over a perceived US and Iraqi failure to crack down on the PKK bases.

After emergency talks Sunday night, a statement by top civilian and military leaders said Turkey was determined to destroy the PKK's safe haven in northern Iraq "whatever the price may be."

Before the talks, Erdogan spoke to US Secretary of State Condoleezza Rice who appealed for patience.

Rice asked for "a few days' time", Erdogan said.

Sunday's PKK attack triggered clashes near the border in which the Turkish military said it had killed 32 separatists.

An advisor to Iraqi Prime Minister Nuri al-Maliki said Turkish Foreign Minister Ali Babacan would visit Baghdad on Tuesday for talks with Iraqi leaders about the current crisis. There was no immediate confirmation of the trip from Ankara.

Iraqi ministers briefed parliament in a crisis session on Monday on government moves to prevent the Turkish incursion and crack down on the rebels.

Iraqi President Jalal Talabani, a Kurd, has said delivering PKK leaders to Turkey is an unrealistic proposition given that the rebels are holed up in remote mountainous areas.

And Massud Barzani, the head of the autonomous Kurdish region in northern Iraq, has warned that his forces would repel any Turkish incursion.

Both leaders were pilloried in the Turkish press on Monday.

"They are no different from Apo," headlined the popular daily Vatan, using the nickname of jailed PKK leader Abdullah Ocalan.

"Enough is enough," the daily Cumhuriyet trumpeted, while Hurriyet wrote: "An operation is now inevitable."

Ankara says some 3,500 PKK rebels are based in northern Iraq, obtaining weapons and enjoying the support of Iraqi Kurdish leaders, a charge the Iraqi Kurdish administration strongly denies.

Erdogan said late Sunday that Ankara "will not hesitate to act under the right military conditions," but his defence minister Vecdi Gonul said after talks with his US counterpart Robert Gates in Kiev that there were no immediate plans to cross the border.

The United States strongly opposes any unilateral Turkish military action, fearing it would further destabilise the situation in Iraq.

More than 37,000 people have been killed since since the PKK launched its insurgency in 1984.