Islamic State militants appear to have beheaded one of their two Japanese hostages and are demanding the release of a convicted terrorist in Jordan in exchange for the other.

A video footage posted online on Saturday showed a still image of one of the hostages, journalist Kenji Goto, holding a photo of what appeared to be the dead body of another captive, Haruna Yukawa, a self-described military contractor.

The voice of a person claiming to be Goto spoke over the image, saying in English that Japanese Prime Minister Shinzo Abe was to blame for Yukawa's death.

A Japanese government spokesman told reporters on Sunday the authorities were still analyzing the video to verify its authenticity.

The jihadist group had demanded that Japan pay a ransom of USD 200M by Friday to spare the lives of the two hostages.

"You were given a deadline," Goto said in the video.

Japan said on Monday it is working to coordinate efforts with Jordan and other countries to save the second hostage.

"We all have one unchanged goal and we will absolutely not give up until the end. And with that faith, we will try our utmost to reach that goal," said Yasuhide Nakayama, a Japanese deputy foreign minister sent to Amman, Jordan, to work on the crisis.

In the video, the voice of Goto said the militants want the release of Sajida al-Rishawi, who faces death penalty for her role in a suicide hotel bombing in Amman, Jordan, in 2005 that killed 60 people.

“It is simple: You give them Sajida, and I will be released,” Mr. Goto said.

Abe announced USD 200M in humanitarian aid to the nations fighting the Islamic extremists earlier this month.