"It is no surprise. We were expecting this decision," one of Ocalan's lawyers, Hatice Korkut, told AFP.

She said an appeal was possible, but Ocalan's defense team would study the court's ruling before deciding how to proceed.

Ocalan, leader of the separatist Kurdistan Workers' Party (PKK), qualifieed as a terrorist group by Ankara and much of the international community, had asked for a retrial in January.

His request poses a legal challenge to the government because current laws do not allow for his retrial, although Ankara is under pressure to comply with ECHR rulings.

A 2003 law that allows for the review of sentences condemned by the ECHR sets a timeframe for admissible applications that explicitly excludes Ocalan's case.

"The parliament must amend this provision because it is clearly in breach of the principle of equality," Korkut said.

A possible retrial could unleash fierce public anger in Turkey, where Ocalan is widely seen as public enemy number one.

The issue has become even more explosive in recent weeks amid increasing PKK violence and a major military build-up against the rebels in the mainly Kurdish southeast.

Ocalan, 57, was condemned to death in 1999 for treason, but his sentence was commuted to life imprisonment in 2002 after Turkey abolished capital punishment as part of efforts to align with European Union norms.

The ECHR ruled last May that the court that convicted Ocalan was not impartial because it included a military judge during part of the trial and because Ocalan and his lawyers lacked sufficient time and opportunity to prepare their defense.

Ankara has said it will respect the ruling, but the authorities have so far failed to say how they will proceed.

Officials have said a possible retrial will seek to correct procedural flaws but cannot result in a lighter verdict for Ocalan.

The Kurdish conflict in Turkey has claimed some 37,000 lives since the PKK took up arms for self-rule in the southeast in 1984.