UK & World News
Reports: Second US Journalist Beheaded By IS
The US and UK are investigating a video which purportedly shows the beheading of US hostage Steven Sotloff by an Islamic State militant who warns that a British hostage will be next.
Mr Sotloff was last seen in Syria in August 2013 but last month he appeared in a video released online by the Islamist group which showed the murder of fellow American journalist James Foley, who was beheaded.
In that video, the 31-year-old was threatened with death unless the US stopped airstrikes aimed at IS in Iraq.
In Tuesday's footage, carrying the title A Second Message To America - and released just days after his mother Shirley pleaded for his release - the freelance journalist is dressed in a similar orange jumpsuit.
A masked militant in the video, with an English accent, tells governments to back off "this evil alliance of America against the Islamic State" - and warns that a British hostage. who is shown kneeling at knifepoint, will be targeted next.
The extremist says: "I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State... despite our serious warnings."
Sky's US Correspondent Dominic Waghorn said that according to Site - a US video monitoring agency in Maryland - the video showed Mr Sotloff being beheaded by the same man, believed to be British, who killed Mr Foley.
Sam Kiley, Sky's Foreign Affairs Editor, watched the video and said: "The killer is holding an identical knife, standing just behind and to the left of Mr Sotloff.
"He is also armed with a shoulder holster identical to the one that carried a pistol on his last video, just prior to the murder of James Foley.
"He has got exactly the same accent... but it is clear that the voice has been somehow treated or adjusted.
"There is some kind of disguising mechanism that has been put to use to try to further hide his identity in addition to the black mask that reveals only his eyes."
White House spokeswoman Jen Psaki said: "The intelligence community will work as quickly as possible to determine its authenticity.
"If the video is genuine we are sickened by this brutal act, taking the life of another innocent American citizen. Our hearts go out to the Sotloff family."
She would not be drawn on whether current events meant the US was at war with IS, formerly known as ISIS and ISIL, which has claimed territory across Syria and Iraq and declared itself a caliphate.
British Prime Minister David Cameron, who will be chairing a meeting of the Government's emergency committee Cobra on Wednesday morning, said: "If verified, this is a despicable and barbaric murder.
"We have already been working hard to keep British people safe and we will continue to do all we can to protect our country and our people from these barbaric terrorists."
The Foreign Office said it was also "urgently working to verify the authenticity of the video".
Mr Sotloff's relatives said they were aware of "this horrific tragedy" and were "grieving privately".