"The Turkish Armed Forces have unshakable determination to combat terrorism and it... will give the necessary response to such attacks," the General Staff said in a statement posted on its Internet site.

The statement came after rebels from the outlawed Kurdistan Workers' Party (PKK) detonated a landmine by remote control on a rural road near the town of Sirvan, in Siirt province, late Thursday as a military vehicle was passing.

Three soldiers were immediately killed in the blast and fourth died in hospital early Friday, local security sources said.

Two other soldiers were wounded in the attack.

Siirt is one of three southeastern provinces where the army has set up temporary security zones as part of a major operation to crack down on PKK rebels.

Violence has escalated in the mainly Kurdish east and southeast of the country amid a military crackdown on PKK rebels who, Ankara says, launch attacks on Turkish targets from their bases in the Kurdish-held autonomous north of Iraq.

The military operation involving thousands of troops has triggered speculation that the army is poised to enter northern Iraq to chase the rebels.

Turkish soldiers killed a PKK rebel in the eastern province of Bingol during the ongoing security sweep, the local governor's office said Friday.

More than 37,000 people have been killed since 1984 when the PKK, listed as a terrorist group by Ankara and much of the international community, took up arms for self-rule.

The general staff said Turkey's national unity was under threat and called on the nation to react against the "separatist and racist terrorist organization."

"The time has come for individuals and institutions who... at home and abroad, cite superior human values such as peace, freedom and democracy as a screen for the terror organization, to see what truly lies behind these events," the statement said.

Turkey, which is seeking to join the European Union, often accuses its European allies of ignoring the activities of organizations linked to the PKK on their own soil.

Ankara says the PKK obtains much of its finances through drug trafficking, people smuggling, extortion and money laundering in Europe.