Japan's Prime Minister Shinzo Abe ruled out giving in to demands of terrorists, condemning as "outrageous and impermissible" the apparent death of a Japanese hostage, Haruna Yukawa, at the hands of Islamic State militants.

Abe again called on the terrorist group to free journalist Kenji Goto, the second Japanese national they are holding.

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On Sunday, IS militants put up a website video of Goto showing photos of what appeared to be the image of Yukawa beheaded.

In the clip, a male voice that appeared to be that of Goto's played in English and subtitled in Arabic. The man was accusing Abe of letting Yukawa die.

Goto could be heard saying the militants are no longer interested in a ransom. The hostage said he will be released in exchange for Sajida al-Rishawi, a woman accused of trying to detonate a bomb strapped to her, who is now jailed in Jordan.

U.S. President Barack Obama called Abe on Sunday from India's capital to offer his sympathy and thanked the Japanese prime minister for the humanitarian aid delivered to the Middle East.

Over the weekend, Obama pledged to bring to justice the perpetrators of Yukawa's "brutal murder."

On Saturday, U.S. Secretary of Defense Chuck Hagel pointed out how the Islamic State's "inhumanity" compares to the much-needed humanitarian aid that Japan has handed out to Syrians and Iraqis in recent weeks. He said the militants' barbarism could only unite nations taking part in a global coalition to end the terrorist group.

Islamic State fighters, who now hold sway over several areas across Iraq and Syria, posted a video on Tuesday threatening to behead the Japanese hostages within three days unless Tokyo pays them $200 million.

Abe vowed to do everything in his power, including seeking the help of Syrian authorities, to free the captives. The White House also announced it will take "decisive" action to thin out the ranks and eventually defeat Islamic State fighters.

TagsISIS, Haruna Yukawa, Kenji Goto