Turkish troops killed 20 Kurdish guerillas yesterday in a major operation against separatist rebels in eastern Turkey, army sources said.

The operation involved 8,000 troops with air support in the eastern province of Tunceli, hundreds of kilometres from the Iraqi border. The source gave no details on army casualties.

Ankara also feels threatened by Kurdish separatists using bases in mountainous northern Iraq for attacks on Turkey, and Turkey's Foreign Minister said a military solution was still on the table to tackle these rebels.

The outlawed Kurdistan Workers Party (PKK) has killed about 40 people in the past month, including 12 soldiers in the latest major attack, and said it took eight soldiers prisoner.

In Istanbul, police in riot gear and armoured vehicles scuffled with demonstrators calling for the PKK's jailed leader to be freed and protesting against an incursion into northern Iraq. Protesters hurled petrol bombs after some 200 people marched chanting through the streets.

In nearby Izmit, three people at an anti-PKK demonstration were slightly injured by an explosion which bomb experts were investigating, the state news agency Anatolian reported. Other demonstrations were held across the country.

Ankara is under strong domestic pressure to deal with the PKK, but Turkish-Iraqi talks aimed at preventing a cross-border incursion collapsed on Friday after Ankara rejected Iraq's proposals as insufficient.

Turkey has massed up to 100,000 troops, backed by fighter jets, helicopter gunships and tanks on the border for a possible offensive against an estimated 3,000 rebels based in Iraq.

The army sent more equipment to the border yesterday although army sources said preparations were almost complete.

Alongside diplomatic initiatives, Turkey has used tough rhetoric to try to press the US and Iraq into action. Prime Minister Tayyip Erdogan said on Saturday a military operation could be carried out whenever it was needed.