By Kathleen Hennessey, Los Angeles Times

TALLINN, Estonia — U.S. intelligence officials have verified the authenticity of a video showing the beheading American journalist Steven Sotloff, President Obama said Wednesday as he declared the U.S. would “not be intimidated” by the Islamic State militants’ acts of “barbarism.”

“Whatever these murderers think they’ll achieve by killing innocent Americans like Steven, they have already failed,” Obama said. “We will not forget, and our reach is long and justice will be served.”

The Sunni militant group released the video Tuesday purportedly showing Sotloff shortly before and after his death. In the video, a black-clad militant declares that Sotloff’s killing was retaliation for the U.S. airstrike Obama has ordered on Islamic State targets in northern Iraq.

“Just as your missiles continue to strike our people, our knife will continue to strike the necks of your people,” the man says.

The video was released hours before President Obama left Washington for Estonia, where he is meeting with Baltic leaders before heading to Wales for a NATO summit. At a press conference Wednesday morning, Obama expressed his condolences for Sotloff’s family and praised Sotloff as a journalist who “deeply loved the Islamic world.”

Sotloff, a 31-year-old freelance journalist who wrote for such outlets as Time magazine and Foreign Policy, was kidnapped shortly after crossing into Syria in August 2013. Two weeks ago, he appeared in video showing the beheading of fellow American journalist James Foley. In that video, a militant in a similar black mask and speaking English with British accent threatened that Sotloff would be next.

Obama has continued the air campaign against the group despite the threats. The Islamic State has seized large pieces of northern and western Iraq in its campaign to establish a caliphate across the region.

Unlike some nations, the U.S. does not negotiate or pay ransom for hostages, officials say. Earlier this summer, Obama authorized a raid on an Islamic State camp in Syria in an attempt to rescue Sotloff, Foley and others believed to be to held by the group, but no hostages were found at the site.

Obama has said he is considering striking Islamic State forces in Syria, although he acknowledged he hopes to more fully develop a strategy for such action as he consults with allies in coming days.

Asked Wednesday whether his goal was to destroy the group, also known as ISIL, or merely contain it, Obama tried to set realistic aims. He compared the group to al-Qaida, saying “there’s always going to be remnants that can cause havoc.”

“Our object is to make sure that ISIL is not an ongoing threat to the region and we can accomplish that,” he said. “It’s going to take some time; it’s going to take some effort.”

AFP Photo/Nicholas Kamm