Reporters Without Borders (RSF) has urged Ankara to release the international rights group's Turkey representative and two other activists arrested on "terror propaganda" charges.

The RSF secretary general, Christophe Deloire, made the call while leading a demonstration Friday outside Metris prison, where the trio is held in Istanbul.

About 30 people took part in the protest, carrying pictures calling for the release of the detainees.

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

"The attacks on freedom of the press are more and more serious and even the expressions of solidarity are being fought against," he said.

On June 20, the RSF Turkey representative, Erol Onderoglu, along with journalist Ahmet Nesin and the rights activist, Sebnem Korur Fincanci, were charged with "terror propaganda" after guest-editing pro-Kurd newspaper Ozgur Gundem.

Prosecutors have called for jail sentences of up to fourteen-and-a-half years for the three campaigners.

The head of RSF, which has already ranked Turkey 149th out of 180 countries in its latest World Press Freedom Index, said Onderoglu falls victim to the "absurd situation."

The arrests came 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 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.