The father of the Japanese hostage apparently killed by Islamic State has said he is overwhelmed by grief.
Shoichi Yukawa said he still had hope "deep in my heart that this is not true" and added that if he were reunited with his son he would give him a "big hug".
Prime Minister Shinzo Abe slammed "an outrageous and unforgivable act" after a video reportedly showing an image of captive Kenji Goto holding a picture of a beheaded Haruna Yukawa was posted online.
The clip also purportedly contained the voice of journalist Mr Goto, 47, claiming the 42-year-old private military company operator had been killed.
Mr Abe said the video, which also includes a demand for a prisoner exchange for Mr Goto, appears to be authentic.
The jihadist group Islamic State (IS) had threatened to kill the captives unless a $200m (£133m) ransom was paid to secure their release.
The 72-hour deadline set by the Islamist militants expired on Friday.
However, in the new video they have called for the release of Sajida al Rishawi, an Iraqi woman sentenced to death in Jordan for her part in the Amman bombings in 2005 that killed 60 people.
Mr Abe insisted Tokyo would not bow to terrorism and said his government would spare no effort to secure the release of the remaining captive.
But he reiterated that Japan would not give in to terrorism.
Barack Obama condemned the "brutal murder" and said the United states would stand "shoulder to shoulder" with Japan.
He called Mr Abe to offer his condolences and called for the immediate release of Mr Goto.
In the video, Mr Goto spoke in English, blaming Mr Abe for Mr Yukawa's death, and told his wife and family not to give up on him.
A Japanese news agency reported the video of Mr Goto had also been emailed to the wife of one of the hostages.
The hostages had appeared in videos wearing the same orange jumpsuits as those worn by captives in previous IS videos.
The mother of Mr Goto has pleaded with militants to spare her son's life.
Junko Ishido said he is a friend of Islam who devoted his life to helping children in war zones.
Mr Yukawa was seized by militants in August, after he went to Syria in what he described as a plan to launch a security company.
Mr Goto, a veteran war correspondent, went into Syria in late October seeking to secure Mr Yukawa's release, according to friends and business associates.