Updated at 4:55 p.m. ET
Japan's Prime Minister Shinzo Abe called the purported beheading of a Japanese hostage by his ISIS captors an "outrageous and unacceptable" act that had left him speechless.
The remarks came after a video surfaced showing what appears to be one hostage holding a photo of his decapitated fellow abductee.
"This is an outrageous and unacceptable act of violence," Abe told reporters as he arrived at his office after midnight for an emergency meeting, according to Reuters. "We strongly demand the immediate release."
The video came to light hours after a Friday deadline for payment of a $200 million ransom passed on Friday.
The video purportedly shows hostage Goto holding a photo of beheaded fellow captive Haruna Yakawa. (The video, not yet confirmed, is graphic. It can be viewed here.)
In it, a still photo of journalist Goto holding the photo is accompanied by an audio voice-over purporting to be Goto: "They no longer want money," the voice says in halting English of the captors.
"So, you don't need to worry about funding terrorists. They are just demanding the release of their imprisoned sister, Sajida al-Rishawi," the voice-over says.
Al-Rishawa is a would-be suicide bomber who reportedly took part in the 2005 Anman bombings but survived when her vest failed to detonate. She was convicted and sentence to death in Jordan in 2006 but is awaiting an appeal.
After an emergency Cabinet meeting, Abe said in a statement that he was "fully aware of [the] unbearable pain and sorrow" that Yakawa's family must be experiencing. "I am simply left speechless," he said.
"The Government of Japan will never give in to terrorism," he added.
The kidnappers gave Abe 72 hours to produce the ransom to prevent Goto, 47, and Yakawa, 42, from being executed. That deadline passed on Friday and there has been no confirmed word from the captors.
U.S. National Security Council spokesperson Patrick Ventrell said the intelligence community "is working to confirm [the video's] authenticity," adding that the U.S. strongly condemns actions of the self-declared Islamic State, or ISIS.
President Obama condemned the murder of Yakawa, saying in a statement: "We stand shoulder to shoulder with our ally Japan."
"We will work together to bring the perpetrators of these murders to justice and will continue to take decisive action to degrade and ultimately defeat ISIL," the president said, referring to ISIS.
Earlier, Yasuhide Nakayama, a deputy foreign minister sent to Amman, Jordan, was quoted by The Associated Press as saying he "is working around the clock to coordinate efforts to save the hostages."
"We will not rule out any possibility, and we are verifying all information thoroughly," he said, according to the AP. "We will not give up. I believe it is my duty to ensure we will definitely get them back home, and I will do my utmost to do so."
The Telegraph reports that Abe met Friday with his National Security Council to discuss the crisis as "Japan has scrambled for a way to secure the release of Goto, a journalist, and Yukawa, an adventurer fascinated by war. Japanese diplomats had left Syria as the civil war there escalated, adding to the difficulty of contacting the militants holding the hostages."
As we reported earlier, the $200 million sum demanded by the kidnappers is equivalent to the amount of money Japan pledged in non-military aid to countries in the region facing threats from the Islamic State militancy.