Japan Prime Minister Shinzo Abe on Sunday called the apparent killing of a Japanese captive by Islamic State militants “outrageous and impermissible,” and again called for the release of a Japanese journalist being held by the group.

Abe, speaking to public broadcaster NHK, said chances were high that a recording and an image of what appeared to be the decapitated body of Japanese captive Harman Yukawa, which emerged late on Saturday, were authentic.

Abe also called for the immediate release of the remaining Japanese captive, reporter Kenji Goto, and said he was putting top priority on saving Goto’s life.

But he reiterated that Japan would not give in to terrorism.

“Such an act of terrorism is outrageous and impermissible, which causes me nothing but strong indignation,” Abe said.

“Again, I strongly demand that Mr. Kenji Goto not be harmed and be immediately released. The government of Japan will, in its entirety, do its utmost in order to have him released.”

The sudden escalation of the hostage crisis has become a test for Abe and the dominant news story in Japan since Tuesday when Islamic State militants released a video showing Goto and Yukawa kneeling with a knife-wielding, masked man demanding a $200 million ransom for their release. The 72-hour deadline set in the first video expired on Friday.

In the apparent recording, Goto says Yukawa was “slaughtered in the land of the Islamic Caliphate.” But the journalist said the Japanese government could save him by working through Jordan where Abe earlier this week set up an office to coordinate the government’s response to the hostage situation.

Goto says the militants would release him in exchange for the release of Sajida al-Rishawi, an Iraqi held in Jordan. He says the militants have dropped the ransom demand.

Abe told NHK that he had spoken to Jordan’s King Abdullah about the situation but he had no comment on the Islamic State demand for the release of al-Rishawi.

U.S. President Barack Obama condemned the brutal murder of Yukawa in a statement released by the White House, which did not address how Washington had confirmed his killing.

The Obama statement, issued while he was en route to India, said: “The United States strongly condemns the brutal murder of Japanese citizen Haruna Yukawa by the terrorist group ISIL,” using an acronym to refer to Islamic State.

In a separate statement, U.S. Secretary of State John Kerry also said Washington “strongly condemns ISIL’s despicable murder of an innocent Japanese citizen, Haruna Yukawa.”