Four Turkish academics are going on trial in Istanbul accused of spreading "terrorist propaganda" for signing a declaration denouncing the renewed conflict with Kurdish rebels.

In a separate courtroom also Friday, the closed-door trial resumes for two prominent opposition journalists who are accused of espionage and aiding a terrorist organization for their reports on alleged government arms-smuggling to Syria, as Turkey continues to clamp down on dissenting voices.

The four academics were among a group of more than 1,000 scholars who in January signed a declaration critical of the government's military operations against the Kurdish rebels. The declaration angered President Recep Tayyip Erdogan and led to legal proceedings against some.

The four were arrested last month after holding a news conference during which they stood by the declaration.