The suspect -- a woman in her 30s posing as pregnant -- carried 8.8 kilogrammes (19 pounds) of explosives, 15 detonators and a manual button in her bag when she was arrested in the downtown district of Sisli after a police pursuit, Governor Muammer Guler told reporters.

She was believed to have been preparing for a suicide bombing "because of the belt she was wearing," he said, without elaborating.

The police, he said, established she belongs to the "separatist terrorist organisation" -- a reference to the Kurdistan Workers' Party (PKK), which has waged a bloody campaign for self-rule in Turkey's Kurdish-majority southeast since 1984.

The amount of explosives the suspect carried suggested she was preparing an attack on a scale as "murderous" as two bomb explosions in Istanbul in July that killed 17 people and which were blamed on the PKK, Guler said.

Listed as a terrorist group by Turkey and much of the international community, the PKK has recently stepped up violence, claiming 22 lives in two attacks against the security forces this month.

The first, on October 3, targetted a military outpost at the Iraqi frontier, in which PKK rebels crossing from mountainous hideouts across the border killed 17 soldiers.

On Wednesday, suspected PKK militants machine-gunned a police bus in Diyarbakir, the central city of the southeast, killing five.

The Turkish army said earlier Saturday that its fighter jets bombed PKK positions inside northern Iraq overnight, the sixth such air raid in the region since the assault on the outpost.

The PKK took up arms in 1984, sparking a conflict that has claimed about 44,000 lives.