UPDATED 9.25am: The Islamic State group has confirmed its militants have executed Japanese hostage Haruna Yukawa, following the release of a video announcing his death.

"The Islamic State has carried out its threat... it has executed Japanese hostage Haruna Yukawa after the expiry of the deadline given," the Sunni extremist group said on Al-Bayan radio, which broadcasts in areas under its control in Iraq and Syria.

"The second hostage (Kenji Goto) is calling on his relatives to put pressure on the (Japanese) government for the release of our sister Sajida al-Rishawi, held in the jails of the oppressors in Jordan, in exchange for his release," it said on Sunday.

Rishawi is a would-be Iraqi female suicide bomber on death row in Jordan in connection with triple hotel bomb attacks in Amman that killed 60 people on November 9, 2005.

Her name emerged on Saturday in a video released by the Islamic State that shows images of Goto holding what appears to be a photograph of the slain body of his compatriot Yukawa.

The video was released with an audio recording in which a man claiming to be Goto blames Japanese Prime Minister Shinzo Abe for his fellow captive's death because he failed to pay IS a $US200 million ($A248 million) ransom by the end of the 72-hour deadline it announced on Tuesday.

The voice also reveals a new demand for the release Rishawi, saying the militants are no longer demanding money to save his life, but want "their sister" to be freed.

"It is simple. You give them Sajida and I will be released," the voice says.

Earlier on Sunday, Japan's prime minister Abe branded the murder of Yukawa, a self-employed security contractor, as "outrageous and unforgivable" and demanded IS to immediately release Goto, a freelance journalist.

World leaders have also denounced the murder, with US President Barack Obama calling it "brutal" and British Prime Minister David Cameron branding it "murderous barbarity".

Japan dispatched a minister to Jordan earlier this week but Abe has declined to comment on whether he would ask Amman to release Sajida.