"We have seen a video that purports to be the murder of US citizen Steven Sotloff by the Islamic State of Iraq and the Levant (ISIL). The intelligence community is working as quickly as possible to determine its authenticity," National Security Council Spokesperson Bernadette Meehan said.
"If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends. We will provide more information when it is available," Meehan said after the video surfaced on social media websites yesterday.
If found genuine, this would be the second brutal murder of an American journalists by ISIS, an al-Qaeda splinter group which has seized hundreds of square miles in Iraq and Syria.
"This is something that the administration has obviously been watching very carefully, since this threat against Sotloff's life was originally made a few weeks ago. Our thoughts and prayers, first and foremost, are with Sotloff and Sotloff's family and those who worked with him," White House Press Secretary Josh Earnest told reporters.
"The US has dedicated significant time and resources to trying and rescue Sotloff. I'm not in a position to confirm the authenticity of that video or the reports at this point, obviously, since I just walked out here," he said.
"Our hearts and prayers go out to the family of Sotloff and all those who have suffered under ISIL's barbaric behavior," Senator Lindsey Graham said.
Describing Sotloff as a man of enormous courage and decency, Senator Marco Rubio said through his execution, ISIL has demonstrated yet again its limitless capacity for cruelty and its unbridled hatred of freedom-loving people everywhere.
The Committee to Protect Journalists said the beheadings on camera in a two-week period of first James Foley and then Steven Sotloff appear to be an acceleration of a pattern- dating at least to Daniel Pearl's killing in 2002- of criminal and insurgent groups displaying the murders of journalists to send a broad message of terror.
Leaders of the Maryland Muslim community joined representative of the Council on American-Islamic Relations (CAIR) to condemn the killing of Sotloff by ISIS.
"No words can describe the horror, disgust and sorrow felt by Muslims in America and worldwide at the unconscionable and un-Islamic violence perpetrated by the terror group ISIS. The criminal actions of ISIS are antithetical to the faith of Islam," CAIR said in a statement.
"If the video is genuine, we are sickened by this brutal act taking the life of another innocent American citizen," State Department Spokesperson Jen Psaki told reporters.