PM slams 'barbaric' IS after video
The reported murder of Japanese hostage Haruna Yukawa by Islamic State is "another reminder of the murderous barbarity of these terrorists", David Cameron said.
The Prime Minister said Britain "stands in solidarity with the Japanese people" and he backs the "firm stance" taken by his counterpart in Tokyo, Shinzo Abe.
The Japanese government is seeking urgent verification of the video, which suggests the captive has been executed.
Earlier this week footage was released in which a masked militant, believed to be the Briton known as Jihadi John, made threats to kill the two Japanese hostages unless a 200 million dollar (£133 million) ransom was paid.
Japanese news organisation NHK said the government in Tokyo is looking to establish the authenticity of a new video, released today, in which hostage Kenji Goto Jogo stated that his fellow captive was executed.
The latest footage shows a still image of Mr Goto, 47, with him apparently holding a picture of a beheaded Mr Yukawa, 42.
He speaks in English, blaming Japanese prime minister Mr Abe for Mr Yukawa's death, and telling his wife and family not to give up on him.
Tokyo has refused to say whether the government would pay the ransom but, like the UK, Japan is signed up to the G8's policy of not paying money to terrorists such as IS, also known as Isil.
Mr Cameron said: "The reported brutal murder of Haruna Yukawa and the further threats made by Isil are yet another reminder of the murderous barbarity of these terrorists.
"My thoughts and prayers are with Mr Yukawa's family. Britain stands in solidarity with the Japanese people at this difficult time and we will continue to offer the Japanese government all possible assistance.
"Japan is right to refuse to bow to terrorism. Britain strongly supports the firm stance Prime Minister Abe and his government have taken and we will continue to work with Japan and other partners around the world to promote peace and to build a safer, more secure future for our citizens."
Foreign Secretary Philip Hammond said: "If confirmed, the brutal murder of Haruna Yukawa is a barbaric and despicable act.
"My thoughts are with the family as they come to terms with this terrible news.
"This only serves to underline the depravity of Isil: their brutality cannot be allowed to succeed."
Mr Abe told reporters that the release of the new message was ''an outrageous and unforgivable act''.
He added: "We demand their immediate release."
The hostages had appeared in videos wearing the same orange jumpsuits as those worn by captives in previous IS videos.
Jihadi John has also been present in a number of previous videos in which hostages were both threatened and killed.
British aid workers David Haines and Alan Henning and US journalists Steven Sotloff and James Foley have been beheaded in similar style footage.
British photojournalist John Cantlie has appeared in a number of propaganda videos released by IS, presenting documentary-style clips.
The previous video, released on Tuesday with a promise to execute the hostages unless the ransom was met within 72 hours, is thought to be the first time the group has made a specific demand for cash for hostages.