Prime Minister Shinzo Abe said on Sunday that experts examining a video announcing the killing of Japanese hostage Haruna Yukawa had so far found no reason to doubt its authenticity.

"We have been looking into its authenticity, but unfortunately at the moment we cannot help saying its credibility is high," he told public broadcaster NHK.

He also said government experts were continuing to analyze the recording in an effort to fully confirm its authenticity.

"Considering the unbearable pain and sorrow that his family must be feeling, I am speechless," the prime minister said.

"Such an act of terrorism is outrageous and impermissible, it causes me nothing but strong indignation," he added. "I condemn it strongly and resolutely."

Abe also pledged that Japan would not give in to terrorism.

US solidarity

Earlier, US President Barack Obama said his country "strongly condemns the brutal murder" of Yukawa and stood "shoulder to shoulder with our ally, Japan."

The video, which was posted online on Saturday, shows a still image of Kenji Goto, the other Japanese hostage, holding up a photograph of what appears to be Yukawawa's slain body, along with an audio recording in which Goto says the hostage-takers might spare his life in return for the release of an attempted suicide bomber by Iraq.

pfd/bk (AFP, Reuters, AP)