A video claiming to show what appears to be the body of Haruna Yukawa, one of two Japanese nationals detained by a group believed to be the Islamic State, was posted on the Internet on Saturday night.
The footage consists of the image of a man believed to be Kenji Goto, another hostage, holding a photograph of what is said to be Yukawa's body.
Abe: Likelihood of credibility high
In the audio portion of the video, which is 2 minutes and 52 seconds long, a man's voice says, "I am Kenji Goto Jogo."
The government said it is still trying to confirm the authenticity of the video. However, Prime Minister Shinzo Abe said during an NHK programme Sunday morning that the credibility of the video announcing the execution of one of the Japanese hostages seemed to be high.
"An act of terrorism like this is abominable and unforgivable. I am simply outraged," Abe said on the TV programme. "I condemn it strongly and resolutely ... Given the unbearable pain and sorrow that his family must be feeling, I am speechless."
"It is unfortunate, but at the moment we must say that the likelihood of its credibility is high," he said.
At a press conference Sunday morning, Chief Cabinet Secretary Yoshihide Suga also suggested that the body in the photo was likely Yukawa's.
"We need to study the body before saying with certainty that he was killed," Suga said. "But right now we see no evidence denying the claim."
Titled "This message was received by the family of Kenji Goto Jogo and the government of Japan," the video was posted online shortly after 11 p.m. on Saturday.
In the video, a man dressed in orange clothing who appears to be Goto, says in English: "[Prime Minister] Abe, you killed Haruna. You did not take the threats of my captors seriously and you did not act within the 72 hours."
Then, he says his captors no longer want a ransom.
"They are just demanding the release of their imprisoned sister Sajida al-Rishawi," the man says. "You give them Sajida and I will be released."
Rishawi is an Iraqi woman facing the death penalty in Jordan. She allegedly took part in simultaneous deadly bombings in Amman in November 2005 but survived.
Govt to ask Amman for help in crisis
Government sources said Sunday that Japan is going to request cooperation from the Jordanian government in the release of Goto in light of the new video, which calls for a de-facto hostage swap.
Referring to the change of demand by Goto's captors from a ransom to the release of the female terrorist, Suga said, "The government is asking Jordan and other concerned countries for their cooperation to free Mr. Goto." However, he stopped short of revealing details of the government's request for those countries.
"At the same time, Japan will continue contributing to counterterrorism efforts by the international community without giving in to terrorism," he stressed.
Asked if a deadline has been set for the hostage trade, Suga replied that it has not yet been confirmed.
Though Goto's safety remains unclear, Suga emphasised that the government is doing its best to free him on assumption that he is still alive.
Asked if the voice in the video is really Goto's, Suga said the matter is still being studied.
Obama pledges support over phone
Meanwhile, Abe talked with US President Barack Obama over the phone Sunday afternoon and asked for cooperation in the release of the Japanese hostage, government sources said.
"We are strongly demanding the group to free Mr. Goto immediately without harming him," the sources quoted Abe as telling Obama. "Japan would like to cooperate with the United States [to resolve the crisis]."
Obama pledged US support for Abe, according to the sources.
In a video posted online Tuesday, the group believed to be the Islamic State said the two Japanese nationals would be executed unless a ransom of $200 million was paid within 72 hours.
The amount of the ransom is equal to the amount of humanitarian assistance that Abe pledged to Middle Eastern countries during his most recent trip to the region.