This still image, from video footage posted online by Islamic State militants and provided by the SITE Intelligence Group, purports to show American journalist Steven Sotloff before his death at the hands of a masked man. The Arabic text at the bottom of the frame translates as: "Now is the time for my message."

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

“The US Intelligence Community has analysed the recently released video showing US citizen Steven Sotloff and has reached the judgment that it is authentic,” Hayden said in a statement.

US President Barack Obama is in Estonia ahead of a Nato summit in Wales later this week. - Reuters