Islamic State militants have allegedly killed Kenji Goto, 47, the second Japanese man held hostage by ISIS.
A video was released online that claims to show Goto's death by beheading. The Japanese and U.S. governments are working to authenticate the video, BBC reports.
"We are outraged by this atrocious act," said Japanese Chief Cabinet Secretary Yoshihide Suga, in press conference translated by CNN.
Japan and Jordan were negotiating to release Goto and Jordanian pilot Muath al-Kaseasbeh. ISIS was demanding the release of a failed female suicide bomber, Sajida al-Rishawi.
"We stand in solidarity with our ally Japan," said U.S. National Security Council Spokesperson Bernadette Meehan, in a statement.
Goto was a freelance journalist and filmmaker who NBC reports went to Syria to rescue Haruna Yukawa, also from Japan. Yukawa, 42, was killed by ISIS about a week ago.
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Gavin Stern is a national digital producer for the Scripps National Desk.