Still image from video of Sotloff kneeling next to a masked Islamic State fighter
A video purportedly showing U.S. journalist Steven Sotloff kneeling next to a masked Islamic State fighter holding a knife in an unknown location in this still image from video released by Islamic State September 2, 2014. The Islamic State released a video purporting to show the beheading of Sotloff, a monitoring service said on Tuesday, as the militant group raised the stakes in its confrontation with Washington over U.S. air strikes on its fighters in Iraq. REUTERS/Islamic State via Reut

The Islamic State of Iraq and Syria, or ISIS, has released a video of the beheading of another U.S. journalist, Steven Sotloff. SITE Intelligence Group, a watchdog tracking the web postings of jihadists said Sotloff is the second American beheaded by ISIS. According to a report by the New York Times, Sotloff's family released a statement with the belief that the journalist has died in the hands of the Islamic militant group.

The video showed a masked figure issuing a threat to another British hostage ISIS named as David Haines. The executioner appeared to have the same British accent as the one in the video showing the killing of James Foley on Aug. 19. The latest video also has the same desert background with both hostages wearing orange jumpsuits.

Despite the appeal for mercy by Sotloff's mother, ISIS went on to execute the freelance journalist who was kidnapped one year ago in northern Syria.

The beheading of Sotloff came just two weeks after his fellow journalist, Foley, was executed in the same public manner. Foley's executioner had previously warned that Sotloff would be the next captive to die.

In the video, the purported executioner taunted U.S. President Barack Obama. He addressed the president and claimed that it was his "foreign policy towards the Islamic State" including the continued airstrikes in ISIS-held towns that brought the executioner "back."

"I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State, because of your insistence on continuing your bombings and in Amerli, Zumar and the Mosul Dam, despite our serious warnings," the masked man said.

The man in the video went on to say that the U.S.-led airstrikes continue to cause harm to their people. "So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people", the militant said.

Sotloff spoke in the video and described himself as "paying the price" with his life for Mr Obama's intervention in Iraq.

Speaking for the Sotloff family, Barak Barfi said the family believes the video released by the militant group was genuine. The Sotloff family members will not be giving public comments as they are grieving privately.

White House spokesperson Josh Earnest said he could not declare the authenticity of the video immediately since the U.S. government, together with intelligence authorities, will have to verify the video.

U.S. State Department spokesperson Jen Psaki gave assurances that intelligence agencies will work as quickly as they can to determine the authenticity of the video.

The SITE group said ISIS has hinted it will execute the British captive, Haines. According to reports, two other U.S. citizens are believed to be held captive by ISIS.

The beheading of Sotloff has sparked strong reactions from world leaders.

British Prime Minister David Cameron has condemned Sotloff's beheading and called it "an absolutely disgusting and despicable act by barbaric terrorists."

According to Reuters, Iraqi outgoing foreign minister described the act as a "savage killing." He said the video should be taken as further proof that there is an urgent need for the West and Iraq to defeat ISIS.

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