UPDATE 1-Turkish court orders rearrest of jailed Kurdish politician

(Updates with court decision to arrest Demirtas again)

ISTANBUL, Sept 20 (Reuters) - The release from a Turkish jail of the former leader of the pro-Kurdish Peoples' Democratic Party (HDP) is set to be blocked after a court on Friday ordered his arrest on new terrorism-related charges, the HDP said.

One of Turkey's best known politicians, Selahattin Demirtas has been in jail for almost three years and faces several other legal cases, mainly on terrorism charges, which he denies. He faces being sentenced to 142 years in prison in the main case against him.

A Turkish court ruled earlier this month that he should be released while the main trial continues and the HDP said Demirtas' lawyers had on Friday applied for his release on parole.

Prosecutors then launched a new investigation into him and the other former co-leader of the party and requested their arrest, Demirtas said.

"The decision to re-arrest Selahattin Demirtas and Figen Yuksekdag is the massacring of the principles of universal law once again," the HDP said on Twitter, following the court ruling.

The prosecutor's office in Ankara was not immediately available to comment.

The independence of Turkey's judiciary has been hotly debated in recent years, especially since a crackdown on the judiciary and other state bodies following an abortive coup in July 2016 and after the country switched to an executive presidential system in June last year.

"There is no judiciary, no justice, no law, no judges. Not just for us, for none of you," Demirtas said earlier on Twitter, announcing that the new investigation had been launched.

Critics say courts are under the influence of politics. President Tayyip Erdogan and his AK Party have repeatedly said the judiciary is independent and makes its own decisions. (Reporting by Ali Kucukgocmen and Ece Toksabay; Editing by Toby Chopra)