Prime Minister Shinzo Abe said Sunday that the "credibility" of the online video apparently posted by the Islamic State group Saturday is "high," suggesting Tokyo believes Japanese hostage Haruna Yukawa was actually killed by the extremists as claimed in the clip, which includes a shocking still image of what appeared to be his corpse.

"To our regret, we have no choice but say to the credibility (of the video) is high," Abe said during a live interview with NHK. The prime minister had appeared on the program as earlier scheduled.

"Such an act of terrorism is outrageous and impermissible," Abe said. "I feel strong indignation. I resolutely condemn this."