The death of Medya Cinar follows the suicide of three others in prison, the Peoples' Democratic Party (HDP) official who did not wish to be named told AFP.

A HDP lawmaker, Tuma Celik, also said Cinar had killed herself in a prison in the southeast Mardin province.

But the Mardin public prosecutor's office denied reports of Cinar committing suicide as an act of protest, saying such claims were "biased" and "misleading".

Cinar had been charged with "destroying the state's unity and country's integrity", the prosecutor's office said in a statement, after she was detained in 2016.

The office said Cinar "tried to hang herself" and after she was taken to a hospital, she was pronounced dead. Authorities have launched a probe, it said.

Since a hunger strike launched by Kurdish lawmaker Leyla Guven in the southeastern Kurdish-majority city of Diyarbakir in November 2018, Cinar, Ugur Sakar, Zulkuf Gezen and Ayten Becet have taken their lives.

Guven has been on hunger strike for nearly 140 days.

Gezen hanged himself earlier this month but officials rejected claims he killed himself as part of a protest.

Ocalan co-founded the outlawed Kurdistan Workers' Party (PKK). The PKK has waged an insurgency against the Turkish state since 1984 and is proscribed as a terror group by Ankara and its Western allies.

Ocalan was captured in 1999 and is serving a life sentence on Imrali island, close to Istanbul, after he was found guilty of treason.

He has not had access to his lawyers since 2011. Dozens went on hunger strike calling for access for Ocalan's lawyers and family members.

HDP MP Ayse Acar Basaran on Saturday said that Becet committed suicide "to protest the inhuman, unlawful and illegitimate isolation imposed on Abdullah Ocalan at Imrali".

Cinar was normally held in a prison in the eastern Van province, Celik said.

She was brought to Mardin for a hearing in her trial after being arrested following clashes with authorities in 2016 in Nusaybin, a southern town on the Syrian border.

Nusaybin was under curfew for weeks during a military operation to push Kurdish militants out of the town, where the authorities said they had dug trenches and put up barricades.