The Japanese government has confirmed that a video showing the beheading of hostage Kenji Goto appears to be genuine.
The one minute-long footage was released by Islamic State (IS) on Saturday (31 January).
The video titled 'A Message to the Government of Japan' shows Mr. Goto dressed in an orange jumpsuit, kneeling on the ground as the executor, believed to be Jihadi John, delivers a scripted speech in which he threatens to inflict more brutality on the citizens of Japan.
He says: "Abe, 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, UK and US governments have strongly condemned IS for the latest execution of a hostage.
Japan's Prime Minister Shinzo Abe was visibly upset as he spoke to reporters in Tokyo. "I am extremely angry about these heinous and despicable terrorist acts. We will never forgive terrorists," he said.
"We will cooperate with the international community to make them atone for their crimes."
British Prime Minister David Cameron issued a statement saying it was a "further reminder that ISIL is the embodiment of evil, with no regard for human life".
US National Security Council spokeswoman Bernadette Meehan said: "We have seen the video purporting to show that Japanese citizen Kenji Goto has been murdered by the terrorist group ISIL [IS].
" The United States strongly condemns ISIL's actions and we call for the immediate release of all remaining hostages. We stand in solidarity with our ally Japan."
The family of another IS hostage, Jordanian fighter pilot Lt Mu'ath al Kassasbeh, said they were "devastated" by Mr Goto's murder.
Mr Goto, 47, who was an experienced war journalist, went into Syria in October in the hope of rescuing another Japanese hostage, Haruna Yukawa, an eccentric self-styled security contractor, who had been kidnapped by the brutal Islamist group two months earlier.
The savage killing of the Japanese journalist is the latest in a growing list of foreign hostages murdered by Jihadi John, which includes Haruna Yukawa, British aid workers David Haines and Alan Henning, American journalists James Foley and Steven Sotloff, and aid worker Peter Kassig.