.
The Britain-based Observatory said the reporters 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 ISIS.
The head of the Observatory, Rami Abdurrahman, said news of the killings was withheld because no bodies had surfaced and the families feared retribution for reporting the deaths.
In the video, an ISIS 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 ISIS may be targeted, even if they reside in Europe.
Saudi Arabian twins linked to ISIS kill their own mother
Twin brothers in Riyadh have stabbed their entire family - killing their mother and seriously injuring their father and elder brother.
The 20-year-olds are reportedly loyal to ISIS, according to the website RT.
The twins, Khalid and Saleh Al Areeni, allegedly carried out the attack in their family home in the Saudi capital on Friday.
According to investigators, the young men first stabbed their mother with a cleaver and sharp knives brought from outside, before going after their father.
They then chased their elder brother and stabbed him multiple times as well. Having thought the entire family was finished, the twins fled the scene in a stolen car.
The two stabbed men were critically injured and taken to hospital, while the woman died on the spot. Hundreds turned up at the slain mother’s funeral this weekend, Gulf News reported, adding that people prayed for her as they would for a terror victim.
After a large-scale manhunt, police caught the brothers 62 miles from the capital.
According to a statement issued by the Saudi interior ministry, the crime was planned and the twins were found to be loyal to ISIS.
According to local reports, the attackers decided to kill their mother after she found out about their plans to join ISIS. Apparently, the woman told her sons that she would report them to authorities if they kept planning to leave the country.
According to the website, 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 ISIS seized half of Deir el-Zour in 2014.
He said Jawdat had been detained by ISIS on a number of previous occasions.
Since learning of the abduction and killing of the activists the leader said his group has told other activists to refrain from taking photos or shooting video in ISIS-held areas.
Another reporter is understood to have been killed in the same way but with a laptop instead of a camera He is the second to be blown up by equipment rigged with explosives A third is choked to death after being tied to a metal door with an iron chain We have edited the video as some of the footage is too horrendous to show One of the activists apparently worked for Al-Jazeera, while another is understood to have contributed to the New York-based Human Rights Watch.
Neither has yet commented on the killings.
At the same time as news of the journalists’ deaths came, it emerged the Iraqi city of Fallujah has been “fully liberated” by Iraqi troops after being held by ISIS for more than two years.
The news comes as Iraqi military chiefs announce the former ISIS stronghold of Fallujah in Iraq has been "fully liberated" Credit: Getty Images The city has been held by the terror group for more than two years Credit: AP:Associated Press A view of streets in Fallujah after government forces recaptured the city from ISIS militants Credit: Reuters Members of Iraqi government forces celebrate on a street in Fallujah after government forces recaptured the city Credit: Reuters Lieutenant General Abdul-Wahad al Saadi made the announcement on Sunday after his troops entered the northwestern al Julan neighbourhood, the last area under IS control.
He said the campaign, which began in May, "is done and the city fully liberated".
"From the centre of al Julan neighbourhood, we congratulate the Iraqi people and the commander in chief ... and declare that the Fallujah fight is over," al Saadi told Iraqi state TV, flanked by military officers and soldiers.
The announcement was made on Sunday after Iraqi troops entered the last area of the city under ISIS control Credit: Getty Images The fighting had prompted thousands of the city's residents to flee Credit: AP:Associated Press Fallujah was the first Iraqi city to be captured by ISIS Credit: AP:Associated Press Residents celebrated after Iraqi special forces entered the city after fighting ISIS militants Credit: AP:Associated Press Members of Iraqi government forces celebrate on a street in Fallujah Credit: Reuters Iraqi counter-terrorism forces gesture in Fallujah after they took back control of the city from ISIS Credit: Reuters Iraq's Prime Minister Haider al-Abadi is seen during his visit the city of Fallujah after it was liberated Credit: Reuters The fighting had prompted thousands of the city's residents to flee, with some killed by sniper fire from the militants, explosives planted along roads or from drowning in the Euphrates.
Fallujah, 40 miles west of Baghdad, was the first Iraqi city to be captured by ISIS. Along with Mosul, it is one of two major urban areas held by ISIS.
The terror group took control in January 2014, six months before announcing a self-proclaimed caliphate in areas of Iraq and Syria.
The city had a population of more than 320,000 in 2010 but this has dwindled, with estimates at the beginning of the campaign ranging from 50,000 to 70,000.
We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368