Hassan Diab
Hassan DiabReuters

Lawyers and supporters of the chief suspect in a deadly attack on a Paris synagogue in 1980 on Tuesday expressed disappointment at his being denied release for an eighth time.

Hassan Diab, 63, had been ordered released pending the conclusion of the investigation into the case, but the decision was overturned on appeal.

Diab, a Lebanese-Canadian sociology professor, is accused of being part of the special operations branch of the Popular Front for the Liberation of Palestine (PFLP) terrorist group, which carried out the bombing on October 3, 1980 that left four dead and around 40 injured.

Diab has been detained in France since being extradited from Canada in 2014. He claims he is innocent and denies being a member of the PFLP.

Roger Clark, a former director of Amnesty International and member of a Diab support group, told AFP on Tuesday that Diab's continued detention is "extremely disappointing."

"The decision to deny his release reflects the ridiculous nature of what's going on in his case. It's grotesquely absurd," he said.

Clark met with Diab in prison during a recent trip to Paris.

"He expressed a lot of disappointment. Physically he's finding it quite difficult, his health is okay but not great, his mental state is a challenge for him, and he's having difficulty remaining optimistic," Clark said.

The bombing at the synagogue on Rue Copernic in Paris was the first major attack on a Jewish site in France since World War II.

The prosecution has pointed to a sketch of the bomber resembling Diab, the discovery of a passport in his name with entry and exit stamps from Spain, where the bomber is believed to have fled, and testimonies that Diab was a member of the PFLP in the early 1980s.

Diab, however, insists that he was in Beirut at the time of the attack, taking university exams, which witnesses have corroborated.

AFP contributed to this report.