The founder of the outlawed Kurdistan Workers' Party (PKK) had been the sole inmate of a high-security prison on Imrali island until Turkey transferred five other prisoners there about 10 days ago.

Ocalan was also transferred to a smaller cell.

The pro-Kurdish Firat News agency reported that the 61-year-old had told his lawyers that his breathing had been affected.

"I can't breathe here any more because of the ventilation, I suffer from breathing problems. My condition is worse than before," he was quoted as saying.

"I don't know how long I can stay in these conditions which make me feel like a man who is half dead and half alive," he said.

The new inmates were brought to the prison in the Sea of Marmara, northwestern Turkey, after Council of Europe criticism that Ankara was violating Ocalan's human rights by keeping him in solitary confinement.

They are all convicted members of the PKK, media reports said.

Ocalan had been the sole prisoner on the island there since 1999.

According to Turkish law, Ocalan can mix with the new prisoners during a weekly 10 hours of communal activities.

Ocalan, founder and leader of the PKK, was condemned to death for treason and separatism in 1999.

The sentence was commuted to life imprisonment in 2001 following Turkey's abolition of capital punishment as part of reforms to embrace European Union norms.

The PKK is listed as a terrorist group by Turkey and much of the international community. It took up arms in Turkey's mainly Kurdish southeast in 1984, sparking a conflict that has claimed about 45,000 lives.