DUBAI (Reuters) - The Islamic State in Iraq and Syria, better known as ISIS, has raised the stakes in its confrontation with Washington over US air strikes on its fighters with the release of a video that purports to show the beheading of a second American hostage, journalist Steven Sotloff. Observers say appears the video appears to be authentic.
A masked figure in the video also issued a threat against a British hostage, a man the group named as David Haines, and warned governments to back off "this evil alliance of America against the Islamic State", the SITE monitoring service said.
The purported 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 as "paying the price" for the US intervention in Iraq with his life.
Sotloff, a freelance journalist, was kidnapped in Syria in August 2013. His mother Shirley appealed on Aug. 27 in a videotaped message to ISIS self-proclaimed caliph, Abu Bakr al-Baghdadi, for her son's release.
In the video it released last month, the Islamic State, as it now calls itself, said Foley's death was in retaliation for US air strikes on its insurgents who have overrun wide areas of northern Iraq.
The United States resumed air strikes in Iraq in August for the first time since the end of the US occupation in 2011. The raids followed major gains by Islamic State, which has declared an Islamic Caliphate in areas it controls in Syria and Iraq.
In Washington, the White House said it could not immediately confirm that Islamic State had released a video of Sotloff's beheading.
"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 (as ISIS is also know). The intelligence community is working as quickly as possible to determine its authenticity," National Security Council spokesperson Bernadette Meehan said in a statement.
"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."
A source familiar with the matter said that while US officials have yet to formally confirm the validity of the video, it appeared to be authentic.
British Prime Minister David Cameron said the latest video depicted an "absolutely disgusting, despicable act".
Iraq's outgoing foreign minister Hoshiyar Zebari, condemned what he called "this savage killing...an example of savagery and evil." and said this was evidence of the need for Iraq and the West to defeat the ISIS.
"We have a common enemy and the whole world is moving in the right direction to stop this savagery and brutality," Zebari said. "The whole world is standing united against ISIS. They must be defeated so these horrid scenes will not be repeated."
Iraqi Shi'ite Muslim politician Sami Askari, who is close to outgoing Prime Minister Nuri al-Maliki, said: "They are trying to scare the Americans not to intervene. I don't think Washington will be scared and stop ...
"This is evil. Every human being has to fight this phenomenon. Like cancer, there is no cure. You have to fight it."
A person with ties to the Islamic State in Diyala province said the group had suffered badly in northern Iraq since US air strikes began last month, ahead of the filmed execution of Foley and grisly video of the beheading of a Kurdish soldier.
"The defeat of the Islamic State in the battle of Mosul Dam contributed to a deflating of the morale of its fighters and the American strikes have also succeeded in restricting their field operations," the man, who spoke on condition of anonymity, said. "The initiative is not with Islamic State anymore, it's with their enemy now."
The United States is taking the ISIS insurgents far more seriously now than it did six months ago, when Obama told the New Yorker magazine that they were the "JV team", which is short for "junior varsity" and means they are not the best players on the field.
On Aug. 24, al Qaeda-linked Nusra Front militants in Syria freed an American writer, Peter Theo Curtis, who had been missing since 2012, following what officials said were efforts by the Gulf Arab state of Qatar to secure his release.