An internet video released Tuesday night purports to show the beheading of US reporter Steven Sotloff by the Islamic State jihadist group in Syria.

The radical Islamist group threatened to execute British national David Cawthorne Haines next unless its demands were met, Site Intel Group, reported. It was not immediately clear who Haines was. Officials with the British Foreign Office declined to immediately comment.

Sotloff, who freelanced for Time and Foreign Policy magazines, had last been seen in Syrian 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.

A Sotloff family spokesman told the Associated Press that his relatives were aware of the beheading video and are grieving, but that authorities have not established its authenticity.

“The family knows of this horrific tragedy and is grieving privately. There will be no public comment from the family during this difficult time,” Barfi said.

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 is beheaded by an Islamic State fighter.

According to ABC News, the video appeared online on Tuesday and appears to show Sotloff telling the camera: “I’m sure you know exactly who I am by now and why I am appearing.”

“Obama, your foreign policy of intervention in Iraq was supposed to be for preservation of American lives and interests, so why is it that I am paying the price of your interference with my life?” Sotloff said in the video.

The video then cuts to the terrorist who makes a statement saying that as long as US missiles “continue to strike our people, our knife will continue to strike the necks of your people.”

Last month IS executed American reporter James Foley on camera and posted it to the internet, demanding the US halt airstrikes in northern Iraq or it would execute Sotloff.

Sotloff was originally from Miami and had spent the last several years reporting around the Middle East.

White House Press Secretary Josh Earnest told reporters he was unaware of the reports.

“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.”

State Department Spokeswoman Jen Psaki told the press that the US couldn’t immediately confirm the video’s authenticity, and that “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,” Psaki said of the footage. “Our hearts go out to the Sotloff family.”