Online video purports to show Sotloff beheading by ISIS

The American journalist has been held captive by Islamic militants for over a year. The identity of the man beheaded in Tuesday's video has not been confirmed.

An Internet video posted online Tuesday purported to show the beheading of US journalist Steven Sotloff by the Islamic State group, which called it retribution for continued US 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 US 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 purportedly beheaded by an Islamic State fighter.

The Associated Press could not immediately verify the video's authenticity. The SITE Intelligence Group, a US terrorism watchdog, first reported about the video's existence.

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.

At the end of the video, he threatened to kill a third captive, a Briton, David Cathorne Haines.

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 US government actions in the Middle East over which he has no control.

White House press secretary Josh Earnest said he wasn't immediately aware of the purported Sotloff video and wasn't in a position to confirm its authenticity.

"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.