A video purporting to show the execution of hostage Kenji Goto was posted early Sunday morning by the Islamic State of Iraq and the Levant (ISIL) militant group.
Prime Minister Shinzo Abe strongly condemned the apparent killing and reiterated Japan's stance against terrorism, saying, "Japan will never give in to terrorism."
"As a government, we have pursued every possible means to save their lives. We feel greatest sorrow and profound grief. I am infuriated by these inhumane and despicable acts of terrorism, and resolutely condemn these impermissible and outrageous acts," Abe said in a statement.
"We will further expand our humanitarian assistance in the Middle East in areas such as food and medical care." The statement was also released in English and Arabic.
In the 67-second-long video, a masked ISIL militant says in English: "Abe, because of your reckless decision to take part in an unwinnable war, this knife will not only slaughter Kenji, but will also carry on and cause carnage wherever your people are found.
"So let the nightmare for Japan begin."
The government called a meeting of ministers concerned at the Prime Minister's Office on Sunday morning.
"Taking everything into account, [the image] is highly likely to be that of Mr. Goto," Chief Cabinet Secretary Yoshihide Suga said at a press conference shortly before noon.
The government learned of the video at about 5 a.m. and contacted Goto's family.
Suga arrived at the Prime Minister's Office about half an hour later to gather and analyse information with government officials including Deputy Chief Cabinet Secretary Kazuhiro Sugita and Yasuhiko Nishimura, deputy chief cabinet secretary for crisis management. Abe joined them there a few minutes later.
While stressing Japan's stance of fulfilling its responsibility to fight terrorism with the international community, Suga ruled out the possibility of using the Self-Defence Forces to provide logistic support to US-led airstrikes against ISIL.
Asked whether the government had directly contacted ISIL during the hostage crisis, Suga explicitly denied it. "There was no such action," he said.
Foreign Minister Fumio Kishida said he repeated instructions to Japan's overseas establishments to make every effort to secure the safety of Japanese expatriates.
Goto, a 47-year-old freelance journalist, is believed to have entered Syria last October.
The hostage crisis surfaced after the militant group released an online video on Jan. 20, threatening to kill Goto and fellow Japanese hostage Haruna Yukawa, 42, unless the Japanese government paid $200 million in ransom within 72 hours.
A few days later, after a video was released of Goto holding a photograph purporting to show Yukawa's body, the demand was changed from the ransom to the release of a death-row inmate in Jordan named Sajida al-Rishawi, an Iraqi suicide bomber who failed to detonate her explosives.
Later, in a voice message, the group set a new deadline of sunset Thursday for the Jordanian government to bring Rishawi to the Turkish border in exchange for Goto's freedom.
It also threatened to kill Muath al-Kasaesbeh, a Jordanian Air Force pilot captured by ISIL in December, unless the demand was met.