A Turkish court was due Friday to decide whether to release journalists from the opposition newspaper Cumhuriyet jailed on charges of supporting "terrorism", in a trial seen as a test for press freedom under President Recep Tayyip Erdogan.

The trial in Istanbul of 17 writers, cartoonists and executives from the paper began this week and judges will later make an interim ruling on a request by the defence that they should be freed ahead of the next stage of the trial.

The defendants include some of the biggest names in Turkish journalism including Cumhuriyet's editor-in-chief Murat Sabuncu, commentator Kadri Gursel, investigative reporter Ahmet Sik and cartoonist Musa Kart.

They are charged with supporting in their coverage three groups that Turkey considers terror outfits -- the Kurdistan Workers' Party (PKK), the ultra-left Revolutionary People's Liberation Party-Front (DHKP-C), and the movement of Fethullah Gulen, the US-based preacher who Ankara accuses of ordering a coup attempt.

Supporters say the paper has always taken a tough line against the three groups and is merely being punished for being one of the few opposition voices in the Turkish media.

Eleven of the suspects have been held in jail in pre-trial detention, most of them for more than eight months, with the other six free but still charged.

If convicted, they face varying terms of up to 43 years in jail.