An Islamic State video showing the beheading of American-Jewish journalist Steven Sotloff in reprisal for U.S. air strikes in Iraq is authentic, U.S. National Security Council spokesperson Caitlin Hayden said on Wednesday.

"The U.S. Intelligence Community has analyzed the recently released video showing U.S. citizen Steven Sotloff and has reached the judgment that it is authentic," Hayden said in a statement.

An Israeli foreign ministry spokesman confirmed Wednesday afternoon that Satloff was a dual American-Israeli citizen.

The Islamic State militant group released the video purporting to show the beheading on Tuesday. In the video, a masked figure in the video also issued a threat against a third captive, a Briton, a man the group named as David Haines, and warned governments to back off "this evil alliance of America against the Islamic State", the monitoring service said.

The executioner appeared to be the same British-accented man who appeared in an Aug. 19 video showing the killing of American journalist James Foley, and it showed a similar desert setting. In both videos, the captives wore orange jumpsuits.

"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 ... on Mosul Dam, despite our serious warnings," the man said.

"So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."

In the video, Sotloff describes himself a "paying the price" for the U.S. intervention in Iraq with his life.

President Barack Obama said Wednesday that the United States will not be intimidated by Islamic State militants after the beheading of a second American journalist and will build a coalition to "degrade and destroy" the group.

Sotloff, a freelance journalist, was kidnapped in Syria in August 2013. Sotloff's mother Shirley appealed on Aug. 27 in a videotaped message to Islamic State's self-proclaimed caliph, Abu Bakr al-Baghdadi, for her son's release. 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.

About two weeks ago, the Islamic State, formerly known as the Islamic State in Iraq and Syria, released a video showing the beheading of U.S. journalist James Foley, who had gone missing in Syria nearly two years ago, and images of Sotloff in an orange jumpsuit whose life they said depended on U.S. action in Iraq.

Sotloff was originally from Miami, where his family still lives. After his abduction in Syria about a year ago, his family had sought a news blackout, as has been done in the case of many other abducted journalists. The theory is that by putting the journalist in the international spotlight, the kidnappers will assume they’ve netted someone high-profile and can extort ever-higher sums for their captive’s release.

ma condemns the beheading of journalist Steven Sotloff by Islamic State U.S. President Barack Obama condemns the beheading of journalist Steven Sotloff by Islamic State

Sotloff left Miami to attend a boarding high school, Kimball Union Academy in Meriden, New Hampshire, where he coedited the student newspaper, graduating in 2002, according to a New York Times report. He attended University of Central Florida from 2002 to 2004, during which he wrote for the school paper, the Central Florida Future, the university said.

Sotloff at some point based himself in Yemen, having learned Arabic there, and traveled around the region with a Yemeni mobile number. His career took off during the Arab Spring, during which he published work in TIME, National Interest, Foreign Policy, The Christian Science Monitor, and the Long War Journal, to name a partial list from his Twitter account. He also freelanced for the Jerusalem Report and the Jerusalem Post.

"We refused to acknowledge any relationship with him in case it was dangerous for him," said Avi Hoffman, editor of the Jerusalem Report magazine, which had published Sotloff's work.

Janine Di Giovanni, the Middle East editor of Newsweek, told CNN on Tuesday that Sotloff, whom she considered a friend as well as colleague, “very clever, he was very philosophical, he was aware of the risks.” He was, she added, concerned that he had angered Syrian rebels and that they’d put him on some kind of black list last year.