Three people have been arrested in the Turkish City of Gaziantep over the murder of anti-Isis activist filmmaker Naji Jerf. The 38-year-old was shot dead on 27 December with a silenced pistol in broad daylight outside a restaurant in the city 50 miles (80km) from the Syrian border.

The father-of-two was a film director for Raqqa is Being Slaughtered Silently (RBSS), a group of journalists which reports news from the Daesh stronghold and de facto capital in northern Syria. He was a vocal critic of Isis having directed two documentaries about the jihadists and their brutal supression of activists.

A colleague of his at RBSS, Ahmad Mohammed al-Mousa, was killed in Syria within weeks of Jerf's murder. He was the chief editor at Syria's Hentah publication and was scheduled to leave Turkey for France the week after his murder with his wife and two daughters as their visa for asylum had arrived.

According to the Anatolia news agency, a court in the city of Gaziantep remanded the main suspect and his two accomplices in custody prior to a trial which will take place later this year. They gave no other details as to the suspects' identity.

The gunman are thought to be either Isis militants or sympathisers but no group or affiliate has claimed responsibility for the assassination.

Hentah, say its reports on the "daily lives of Syrian citizens", according to the publication's website and this would bring it into conflict with the extremists.

RBSS is one of the last remaining sources of news operating in Raqqa - even though the Muslim extremists have said that membership of the organisation is punishable by death.

Isis has been blamed in the past for killing both western and local journalists including Ibrahim Abdul Qader, who was beheaded in the Turkish city of Urfa. Another journalist, Fares Hamadi, was killed in the same attack.

Isis published a video afterwards where they warned: "You will not be safe from the knife of the Islamic State. Our hand will reach you wherever you are."

The group that campaigns against Daesh and the Bashar al-Assad regime said on Twitter after he was murdered: "Our movie director Naji Jerf, father of 2 kids, was assassinated by suppressor gun today in Gaziantep."