The Islamic State militant group has released a video purportedly showing the killing of Japanese hostage Kenji Goto, who was kidnapped in Syria in October.

In it, Mr Goto is seen kneeling, as a masked man standing beside him with a knife blames the Japanese government for his slaughter.

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A later shot appears to show his beheaded body.

The Japanese government and the White House said they were trying to authenticate the video.

Earlier, senior Japanese officials said negotiations with IS had become deadlocked.

The governments of Japan and Jordan had been trying to secure the release of Mr Goto and a Jordanian pilot who was also captured by the IS in return for the release of an Al Qaeda member who is being held by Jordan.

The video made no mention of the pilot, who has also been threatened with execution.

A second Japanese captive, Haruna Yukawa, was killed by IS last month.

Mr Goto, a freelance journalist, established a video production company that supplied documentaries on the Middle East and other regions to Japanese television networks, including public broadcaster NHK.