Human Rights Watch said in a statement released on Wednesday that, if confirmed, the execution of American journalist James Foley by the Islamic State one day earlier would be a war crime.
The statement comes in response to a video posted on Tuesday by the Islamic State, a Jihadist group formerly known as the Islamic State in Iraq and Sham, showing Foley being executed in Syria. In the video, IS also said they would execute another reporter unless the United States stops air strikes in Iraq.
Foley is a freelance journalist who was seized in Syria in November 2012, and has been missing since then.
Peter Bouckaert, emergencies director at HRW, said that Foley went to Syria "because of his commitment to exposing the horrors civilians faced" during the uprising against Syrian president Bashar Al-Assad's government.
"He, like the other journalists who are now held prisoner in Syria, courageously risked his life so that the world might know the truth and act to ease the suffering of the Syrian people," Bouckaert said.
HRW called on government authorities and non-government armed groups to "immediately release and stop arbitrarily arresting, abducting and detaining journalists as well as human rights activists, humanitarians, and medical professionals for their legitimate work."
HRW pointed out that, earlier this year, the United Nations Security Council unanimously adopted Resolution 2139, which demanded the release of all arbitrarily detained people in Syria.
At least 69 journalists have died while documenting the Syrian conflict, while over 80 have been kidnapped and another 20 are still missing, making Syria the most dangerous country in the world for journalists, according to the Committee to Protect Journalists, the report mentioned.
The international rights organisation expressed its "deep condolences to the Foley family for the tragic loss for their brother and son."
US President Barack Obama also joined HRW in condemning the IS's actions by calling for the elimination of jihadist terror in Iraq and Syria through joint efforts.