Dozens of Turkish demonstrators have protested in Istanbul over the arrests of two journalists and an academic on charges of disseminating "terrorist propaganda."

A Turkish court on Monday ordered the pre-trial arrest of Reporters Without Borders' Turkey representative Erol Onderoglu, journalist Ahmet Nesin and academic Sebnem Korur Fincanci.

The three had participated in a solidarity campaign in support of Ozgur Gundem, a pro-Kurdish publication subject to multiple investigations and lawsuits.

The state-run news agency said the three acted as chief editors for a day for the publication and the issues they edited in May and earlier in June included alleged terrorist propaganda.

Anadolu Agency also said the court ordered the suspects' arrest on "strong criminal suspicion."

Press freedom advocates warn that freedom of expression has dramatically declined in Turkey.