A Turkish court has dismissed a legal bid seeking the release of two journalists and an academic, who are held on “terror propaganda” charges, says the media rights group Reporters Without Borders (RSF).

On Monday, RSF Turkey representative and journalist Erol Onderoglu, journalist Ahmet Nesin, and human rights activist and academic Sebnem Korur Fincanci were charged with "terror propaganda" after guest-editing the pro-Kurdish daily Ozgur Gundem.

The three campaigners have been held in Metris prison in Istanbul. Prosecutors have demanded that they be given jail terms of up to fourteen-and-a-half years.

“The request lodged on Thursday for their liberty has been rejected,” the RSF secretary general, Christophe Deloire, said.

“It's a punitive measure to have them detained and it's another punitive measure to keep them there,” he added.

On Friday, Deloire led a protest outside the gates of the Istanbul jail, with demonstrators holding pictures calling for the release of the trio.

Deloire criticized President Recep Tayyip Erdogan for the “infernal spiral" where both reporters and those who defend their rights were being imprisoned.

Also on Saturday, people took to the streets of Istanbul to protest the arrest of the three campaigners, holding copies of pro-Kurdish newspaper Ozgur Gundem. The Turkish daily has for weeks invited guest editors to take control of the newspaper.

European Union foreign policy chief Federica Mogherini and Enlargement Commissioner Johannes Hahn released a statement on June 20, saying the activists’ arrests run counter to “Turkey's commitment to respect fundamental rights, including freedom of media.”

In a statement released earlier this week, the RSF said arrests marked a new stage “in the criminalization of human rights activism and the continuing decline in media freedom in Turkey, which is ranked 151st out of 180 countries in RSF's 2016 World Press Freedom Index.”

The arrests come despite increasing pressure by the European Union on Turkey to narrow its definition of terrorism. The EU says the law, which has targeted scores of academics, journalists and rights activists, should change if Ankara wants free-visa travels to EU for Turks.

In response to international criticism, Turkey says it sees “no difference” between individuals carrying weapons and those indulging in the spread of "terrorist" propaganda.

For the past two years, Turkey has been tightening its grip on media, especially those sympathizing with the Kurdistan Workers' Party (PKK) militant group. The military has launched a massive crackdown against the PKK in areas close to borders with Iraq and Syria in the south. Offshoots of the PKK have responded by carrying out deadly attacks in the capital, Ankara, and in Istanbul.