A Syrian activist who produced documentaries hostile to the Islamic State group was assassinated in Turkey on Sunday, according to the group with which he worked, “Raqa is Being Slaughtered Silently”, reported AFP. “Filmmaker Naji Jerf, the father of two children, was assassinated… today in Gaziantep”, on the border with Syria, with a silencer-equipped pistol, the group said in a statement on Twitter.

According to CPJ, Turkish authorities said they have opened an investigation. The killing comes after Islamic State claimed responsibility for the deaths of two Syrian journalists found murdered in an apartment in the city of Urfa in southeastern Turkey, near the Syrian border, in October.

“Syrian journalists who have fled to Turkey for their safety are not safe at all,” said Sherif Mansour, CPJ’s Middle East and North Africa program coordinator. “We call on Turkish authorities to bring the killers of Naji Jerf to justice swiftly and transparently, and to step up measures to protect all Syrian journalists on Turkish soil.”

RBSS is a group of citizen journalists who work to expose human rights abuses in Raqa, the northeastern city that IS uses as its de facto capital in Syria.

A friend of Jerf’s said he had been “supposed to arrive in Paris this week after receiving, along with his family, a visa for asylum in France”. Jerf was also editor in chief of Hentah, a Syrian magazine that reports on the “daily lives of Syrian citizens”, said the publication’s website.

This is not the first time a Syrian occupation figure has been murdered in Turkey. At the end of October, IS claimed responsibility for killing militant Ibrahim Abdelkader and a friend. They were found decapitated in a house in Sanliurfa in southern Turkey.

Jerf had recently directed and produced a documentary in which he documented the killing of Syrian activists at the hands of Islamic State during the militant group’s occupation of the city of Aleppo in 2013 and 2014. The documentary, which he published on his YouTube channel this month and which recently aired on pan-Arab satellite channel Al-Arabiya, attracted more than 12 million views and tens of thousands of comments on Al-Arabiya’s Facebook page, Al-Arabiya reported.

Jerf had also directed a documentary about the Syrian citizen journalist group Raqqa is Being Slaughtered Silently, according to the group, which was honored in November with CPJ’s 2015 International Press Freedom Award.