President Barack Obama has vowed the US will not be intimidated, after Islamic State militants released a video showing the beheading of American journalist Steven Sotloff. Mr Obama warned: "Our reach is long and justice will be served." Another US journalist, James Foley, was similarly killed last month. Separately, the UK held a meeting of its emergency Cobra committee after threats to kill a British hostage who was also shown in the latest video. US National Security Council spokesperson Caitlin Hayden said that US intelligence agents had "analysed the recently released video showing US citizen Steven Sotloff and has reached the judgment that it is authentic".