During the visit by a seven-strong delegation of lawmakers and one of his legal team, Ocalan is expected to make a long-awaited statement which they will relay at a news conference at 5:00 pm (1400 GMT) in Istanbul.

"The DEM party delegation.. set off for Imrali island to hold a third meeting with Mr Ocalan," a party source said, referring to the prison island off Istanbul where the Kurdistan Workers' Party (PKK) founder has been in solitary confinement since 1999.

"If everything goes smoothly, we expect Ocalan to make a historic declaration (on Thursday)," the party said late Wednesday.

The Turkish government is seeking to reset ties with the PKK, which has fought a decades-long insurgency that has claimed tens of thousands of lives.

The delegation, which includes lawyer Faik Ozgur Erol, wanted Ocalan to issue a video message rather a written statement but Justice Minister Yilmaz Tunc ruled that out, Turkish media reported.

- Reception unclear -

Observers said Ocalan was likely to call on his followers to lay down their weapons in favour of a political struggle for democracy.

But the big question is how the call will be received by his followers whose military leadership is mostly based in the mountains of northern Iraq.

The PKK also has fighters who are part of the US-backed Syrian Defence Forces (SDF) in northeastern Syria which is seen as crucial to keeping jihadists at bay.

But the force is under pressure to disarm from Syria's new leaders -- who are close to Ankara -- and also locked in clashes with Turkish-backed militia groups.

Ocalan, 75, has been serving a life jail term without parole on Imrali island since his arrest in Nairobi in February 1999.

Since his detention there have been various attempts to end the bloodshed which erupted in 1984 and has cost more than 40,000 lives. The last round of talks collapsed in a storm of violence in 2015.

After that, there was no contact until October when the hardline nationalist MHP leader Devlet Bahceli offered Ocalan a surprise peace gesture if he would reject violence in a move endorsed by President Recep Tayyip Erdogan.

Since then, he has twice been visited by two DEM lawmakers who then briefed the parliamentary parties on the talks.

The contact has fuelled a growing anticipation that Ocalan will call on his fighters to lay down their arms in exchange for concessions for Turkey's Kurdish minority.

Thursday's delegation includes DEM co-chairs Tulay Hatimogullari and Tuncer Bakirhan, and veteran Kurdish politician Ahmet Turk, 82, who has a long history of involvement in efforts to resolve the Kurdish issue.

Deputy speaker Sirri Sureyya Onder and lawmaker Pervin Buldan, who were both part of the earlier delegations, will also go, as will another DEM lawmaker.