A graphic video has emerged showing the killing of five Syrian media activists captured by the Islamic State group last year.
The Britain-based Syrian Observatory for Human Rights says the five were abducted in October and are believed to have been killed in December over their coverage of events in the eastern Syrian city of Deir el-Zour, half of which is held by IS.
The head of the Observatory, Rami Abdurrahman, said on Sunday news of the detention and killing of the activists was withheld because no bodies had surfaced and the families feared retribution for reporting the deaths.
In the video, an IS narrator says the group is facing a media war and warns against reporting to the "crusaders" and "enemies of God".
The narrator says journalists who report on IS may be targeted, even if they reside in Europe.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Abdurrahman said one of the activists, 28-year-old Sami Jawdat, has been feeding information to the Observatory since the outbreak of the civil war in 2011 and continued to do so after IS seized half of Deir el-Zour in 2014.
He said Jawdat had been detained by IS on a number of previous occasions.
He said that since learning of the abduction and killing of the activists, his group has told other activists to refrain from taking photos or shooting video in IS-held areas.
In the video, each activist explains what he did to report from the area, at times acting it out by shooting pictures or interviewing people in the city's market.
One of the activists says he reports for Al-Jazeera, another says he contributed to the New York-based Human Rights Watch.
There was no immediate comment from either on Sunday.
Syria is the third-deadliest country in the world for journalists after Yemen and Iraq, according to the Committee to Protect Journalists.
At least 95 journalists have been killed in Syria since 2011.
Almost no international news organisations send staff to Syria because of kidnappings by militants, who often kill their hostages.
