Ocalan, 61, is the founder of the outlawed Kurdistan Workers' Party (PKK), which has waged a bloody insurgency for Kurdish independence. He has been serving a life sentence in solitary confinement since 1999 on the island of Imrali.

The offer came as demonstrations in Turkey's mainly Kurdish south-east organised to protest at Ocalan's treatment turned ugly, with Molotov cocktails and stones thrown and dozens held by police, according to the Anatolia news agency.

A 19-year-old suffered a serious head injury from a teargas grenade during clashes with police, who were trying to break up a demonstration in the town of Yuksekova, according to local security sources, and a police officer was injured in the same incident.

Turkey's justice ministry published photos on Friday to show that Ocalan's jail conditions were the same as those of other inmates in high-security prisons.

Ocalan was the sole inmate at the prison on Imrali island until new prisoners arrived last month, after the Council of Europe's Committee for the Prevention of Torture (CPT) criticised Ankara for violating Ocalan's human rights by keeping him in solitary confinement.

"After the transfer of new prisoners to the island prison of Imrali, a CPT delegation has been invited to come evaluate the new conditions" of incarceration, which "conform to international standards," the ministry said in a statement late Friday.

Ocalan's complaints to his lawyers about prison conditions, "which are turning me into a man who is half living and half dead," have triggered protests in the Kurdish community. A big demonstration is planned for Sunday in the main Kurdish city of Diyarbakir.

Ocalan's cause has also been taken up by the country's main Kurdish political party. But the Democratic Society Party (DTP) is feeling its own pressure from legal efforts to ban the movement.

Turkey's Constitutional Court will begin deliberations on Tuesday on the fate of the DTP, founded in 2005 from the ashes of another party which was banned over relations with the PKK, which is considered a terrorist organisation by Ankara and much of the international community.

Turkey's chief prosecutor initiated the case in 2007, arguing the DTP had become a "focal point" of activities against national unity through its links with the PKK.

The court will make its ruling against a backdrop of a government drive to expand Kurdish freedoms in a bid to erode popular support for the PKK and encourage rebels to end the insurgency, which has claimed about 45,000 lives since 1984.

The DTP, which holds 21 seats in the 550-member parliament, says it has "no organic links" with the PKK.

However, it refuses to brand the PKK a terrorist group, party members often uphold the rebels along with Ocalan, and PKK banners are a fixture at DTP rallies.