A court in Istanbul ruled late Tuesday that a German-Turkish journalist and social worker held on terrorism-related charges must remain behind bars.

As the trial of Adil Demirci, a 32-year-old dual German-Turkish national from Cologne, opened on Tuesday, he told the court that he didn't have any links to illegal organizations.

The judge ruled that six other defendants arrested in the case were to be released, but Demirci would remain behind bars, his lawyer told dpa, after a hearing that lasted several hours.

The lawyer said this was disappointing because there were more serious charges against the others.

The case will next come up in court on February 14, 2019.

Demirci was arrested in April in Istanbul. He wrote for the leftist news agency ETHA. He also translated material from Turkish into German and English.

He is accused of being a member of the Marxist-Leninist Communist Party (MLKP), an extreme left group designated as a terrorist organization in Turkey.

According to the indictment, seen by dpa, Demirci took part in "unauthorized demonstrations with Molotov cocktails" on behalf of the MLKP between 2013 and 2016, and in funerals for members of the group.

Some of these memorials were for members of the group's armed faction who had fought in Syria against the Islamic State terrorist group.

Demirci has rejected the terrorism accusations, but admitted in court to being present at the funerals and memorials. He never saw weapons at those events, he said, in which thousands of people participated.

Demirci was flanked by police officers as he testified in court a day before his 33rd birthday. 

The German Foreign Office says that five Germans remain in custody in Turkey for "political reasons."