Islamic State (IS) militants released a video last night purporting to show the beheading of Japanese hostage Kenji Goto, the independent intelligence monitoring group SITE said.

The video comes less than a week after news of the beheading of another Japanese man, Haruna Yukawa.

The Japanese government said last night it was working to authenticate the video which showed a hooded man standing over Goto with a knife held to his throat, followed by footage of a beheading.

Addressing Japanese Prime Minister Shinzo Abe, the man says: "Because of your reckless decision to take part in an unwinnable war, this knife will not only slaughter Kenji, but will also carry on and cause carnage wherever your people are found. So let the nightmare for Japan begin."

The Japanese government had put high priority on seeking the release of Goto, a veteran war correspondent captured by the militants in late October when he went to Syria seeking the release of the other Japanese captive, Yukawa. Previous videos purporting to show Goto had said he would be released if Jordan freed Iraqi would-be suicide bomber Sajida al-Rishawi. Amman said it was willing to free her if it could get assurances of the safety of a Jordanian pilot Muadh al-Kassasbeh held by Islamic State.