Islamic State has executed journalist Kenji Goto, saying it would continue to punish Japan for prime minister Shinzo Abe's pledge to support countries affected by the militant group.
Islamic State released a video showing what appeared to be the beheading of Goto, a war correspondent with two decades of experience covering conflicts.
"I am infuriated by these inhumane and despicable acts of terrorism, and resolutely condemn these impermissible and outrageous acts," Abe said in Tokyo.
"I will never forgive these terrorists. I will work with the international community to hold them responsible for their deplorable acts."
The militants, who had pledged to kill Goto and Jordanian pilot Moath al-Kasassbeh unless Jordan released a failed suicide bomber on death row, threatened Japan with "carnage wherever your people are found".
The group pledged to target Japan because of Abe's offer of $200m (€177m) in humanitarian aid to victims of the fighting in Syria and Iraq.
The video did not mention the fate of Al-Kasassbeh, who was captured in Syria on December 24 after his plane crashed on a bombing run against Islamic State.
The group had set a deadline of January 29 for Jordan to turn over Sajida al-Rishawi, an Iraqi woman whose suicide belt failed to detonate during an attack on hotels in Amman in 2005 that killed dozens.
Jordan said it was willing to free Al-Rishawi if Islamic State gave proof that Al-Kasassbeh was alive and was included in the swap for Goto. Jordan never received that proof.
The killing of Goto brings a tragic end to the almost two- week hostage crisis and came a week after the group killed another Japanese hostage, Haruna Yukawa, a self-styled security consultant. He was murdered after Japan failed to pay a $200m ransom initially demanded by the group.
Goto, who specialised in drawing attention to the plight of children in conflict, was captured by Islamic State after travelling to Syria in October to try to seek the release of Yukawa, who had been taken prisoner months earlier.
"I am in no state to choose my words," Goto's mother, Junko Ishido, said yesterday. "I want them to understand my son's generosity and courage."