A court in Tripoli on Wednesday sentenced four Palestinians to prison terms ranging from 17 to 22 years over their alleged links to Hamas.
The four defendants were accused of "setting up a secret foreign organisation on Libyan territory, arms possession and conspiring against state security."
The Palestinians were arrested on 6 October 2016 from their homes in the capital, Tripoli, and were taken to an unknown destination.
Family sources told Arabi21 news site that they had been denied family visits for two months before their prison sentences were announced.
According to the sources, the detainees suffered daily abuses resulted in one of them losing one of his eyes. One detainee named Marwan who suffers from hypertension and diabetes has been denied his medication.
The four Palestinians used to work for a technology company in the capital, Tripoli.
The detainees' families expressed their "fear that they would be handed over to Israel via a third party" appealing to all concerned bodies to help release them.