The Islamic State group released a video Monday claiming the killings of two Syrian activists in Turkey last week, according to the Associated Press (AP). Ibrahim Abdul-Qadir and Fares Hamadi were reportedly found beheaded in Hamadi's apartment in the city of Sanliurfa, 35 miles from the Syrian border, a group called Raqqa Is Being Slaughtered Silently (RBSS) told Al Jazeera on Friday.

Qadir was the founding member of RBSS, which documents the atrocities of ISIS in Syria. The video, cited by the AP, shows a dark room with Hamadi’s body and his throat being slit, but Qadir is not shown in the video. It was not clear when the footage was shot and when the two activists were killed.

The group warned "apostates" that "the arm of the Islamic State will reach you, wherever you are," AP reported.

The video also said, according to Agence France-Presse, that the two activists were slaughtered because "they conspired with the Crusaders against ISIS" adding: "May every apostate know that he will be slaughtered silently."

Another activist from the group was killed in Syria by ISIS, but this is the first time that an activist has been killed outside the country, Al Jazeera reported, citing another member of RBSS. The activist group accused ISIS of the two killings Friday and said that the latest beheadings were a reminder that the militant group has fighters across the region.

“We all thought Turkey would be safer, but apparently not,” Hamoud al-Mousa, another RBSS member living in Turkey, told Al Jazeera, adding: “Unfortunately, none of us are safe here.” Both the activists had received death threats, a local Turkish newspaper reported.

RBSS, which works through a network of secret correspondents operating in and around ISIS-controlled cities and provides credible accounts of life there, was formed in April 2014 just after ISIS started to take control over Raqqa. Earlier in 2015, the group was given the International Press Freedom Award by the Committee to Protect Journalists.

Johann Bihr, head of the Reporters Without Borders Eastern Europe and Central Asia desk, said in a statement, cited by Al Jazeera: “We urge the Turkish authorities to do whatever is needed to bring his murderers to justice and to closely investigate the possibility that he was killed in connection with his reporting," adding: "The authorities must protect journalists who have sought refuge in Turkey.”