The U.S. says video showing the beheading of American journalist Steven Sotloff is authentic.
An Internet video posted online Tuesday reported to show the beheading of U.S. journalist Steven Sotloff by the Islamic State group, which called it retribution for continued U.S. airstrikes in Iraq.
Sotloff, 31, who freelanced for Time and Foreign Policy magazines, had last been seen in Syria in August 2013 until he appeared in a video released online last month by the Islamic State group that showed the beheading of fellow American journalist James Foley.
Dressed in an orange jumpsuit against the backdrop of an arid Syrian landscape, Sotloff was threatened in that video with death unless the U.S. stopped airstrikes on the group in Iraq.
In the video distributed Tuesday and entitled "A Second Message to America," Sotloff appears in a similar jumpsuit before he was reportedly beheaded by an Islamic State fighter.
The SITE Intelligence Group, a U.S. terrorism watchdog, first reported about the video's existence. Unlike Foley's beheading, which was widely shared on Twitter accounts affiliated with the Islamic State group, the video showing Sotloff's killing was not immediately posted online, though several jihadi websites told users to expect it Tuesday.
The fighter who beheads Sotloff in the video called it retribution for Obama's continued airstrikes against the group in Iraq.
"I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State ... despite our serious warnings," the fighter said. "So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."
At the end of the video, he threatened to kill a third captive, a Briton, David Cawthorne Haines. It was not immediately clear who Haines was.
Sotloff's mother had pleaded for his release last week in a video directed at the Islamic State group.
Addressing the leader of the Islamic State group by name, Shirley Sotloff said in a video her son was "an innocent journalist" who shouldn't pay for U.S. government actions in the Middle East over which he has no control.
"This is something that the administration has obviously been watching very carefully," Earnest said. "Our thoughts and prayers first and foremost are with Mr. Sotloff and Mr. Sotloff's family and those who worked with him."
A man who answered a phone listed in the name of Sotloff's sister hung up when called by the AP.
The Islamic State group which has taken over a third of Syria and Iraq has terrorized rivals and civilians alike with widely publicized brutality as it seeks to expand a proto-state it has carved out on both sides of the border.
In its rise to prominence over the past year, the extremist group has frequently published graphic photos and gruesome videos of everything from bombings and beheadings to mass killings.