ISTANBUL — A Turkish court on Friday again rejected a request for businessman and human rights defender Osman Kavala's release from jail, despite a European Court of Human Rights ruling that called for his freedom. 

The court in Istanbul also ruled to merge two ongoing proceedings against Kavala and adjourned the trial until May 21. 

Kavala, 63, is accused of espionage and attempting to overthrow the government in connection with a failed coup in 2016. Separately last year, he was acquitted of terrorism-related charges for allegedly organizing and financing mass anti-government protests in 2013. But a higher court later overturned the acquittal, paving the way for a re-trial.

He will now be tried both for alleged connections to the failed coup and to the mass protests, and faces life in prison should he be convicted. 

Kavala, who denies the accusations, has been imprisoned since he was detained in October 2017. Human rights groups have denounced the proceedings against him as unjust and politically motivated, and have called for his release. The case is being watched closely as a test of President Recep Tayyip Erdogan's sincerity concerning his pledge to carry out democratic, judicial and economic reforms. 

During Friday's hearing, Kavala requested that he be released on bail, insisting that it was out of the question for him to tamper with any evidence.

"Every day I am detained causes a new rights violation. I demand my release," Punto24 website, which is monitoring the trial, quoted Kavala as telling the court.

Kavala is known for his support of the arts and his funding of projects promoting cultural diversity and minority rights. 

Erdogan, however, has accused Kavala of being the "Turkish leg" of billionaire U.S. philanthropist George Soros, who the Turkish leader alleges has been behind insurrections in many countries.