Japanese Prime Minister Shinzo Abe said Sunday he is "infuriated" by the purported beheading of journalist Kenji Goto by the Islamic State group and vowed to hold the terror group responsible.
"I feel indignation over this immoral and heinous act of terrorism," Abe told reporters after convening an emergency Cabinet meeting.
"When I think of the grief of his family, I am left speechless," he said. "We are filled with deep regret."
Japan ordered heightened security precautions Sunday and said it would persist with its non-military support for fighting terrorism.
Threats from the Islamic State group, also known as ISIS, prompted an order for tighter security at airports and at Japanese facilities overseas, such as embassies and schools, government spokesman Yoshihide Suga said.
He said it would be "inappropriate" to comment on the status of the Jordanian pilot.
The failure to save Goto raised fears for the life of the pilot, Lt. Muath al-Kaseasbeh, also held by the militant group that controls about a third of both Syria and Iraq. Unlike some earlier messages delivered in the crisis, the video that circulated online late Saturday purporting to show a militant beheading Goto did not mention the pilot.
Jordan renewed an offer Sunday to swap an Al Qaeda prisoner for al-Kaseasbeh, who was seized after his F-16 crashed near ISIS' de facto capital, Raqqa, Syria, in December.
Jordanian government spokesman Mohammed al-Momani told The Associated Press that "we are still ready to hand over" Sajida al-Rishawi, who faces death by hanging for her role in triple hotel bombings in Jordan in 2005.
Jordan is reportedly conducting indirect, behind-the-scenes negotiations through tribal leaders in neighboring Iraq.
Al-Momani also said his country spared no effort to free Goto.
The killing of Goto, a freelance reporter whose work focused on refugees, children and other victims of war, shocked Japan, which until now had not become directly embroiled in the fight against the militants.
With no updates for days, al-Kaseasbeh's family appealed to the government for information on his situation. But for Goto's family and friends, the beheading shattered any hopes for his rescue.
"Kenji has died, and my heart is broken. Facing such a tragic death, I'm just speechless," Goto's mother Junko Ishido told reporters.
"I was hoping Kenji might be able to come home," said Goto's brother, Junichi Goto, in a separate interview. "I was hoping he would return and thank everyone for his rescue, but that's impossible, and I'm bitterly disappointed."
According to his friends and family, Goto traveled to Syria in late October to try to save Haruna Yukawa, 42, who was taken hostage in August and who was shown as purportedly killed in an earlier video.
"He was kind and he was brave," said Yukawa's father Shoichi. "He tried to save my son."
"It's utterly heartbreaking," he said, crying and shaking. "People killing other people -- it's so deplorable. How can this be happening?"
Abe vowed to continue providing humanitarian aid to countries fighting ISIS. Bowing to terrorist intimidation would prevent Japan from providing medical assistance and other aid it views as necessary for helping to restore stability in the region, he and other officials say.
But the government spokesman, Suga, said Abe would not link the hostage crisis to his efforts to expand Japan's military role in "collective self-defense" with the U.S. and other allies.
The White House released a statement in which President Barack Obama also condemned "the heinous murder" and praised Goto's reporting, saying he "courageously sought to convey the plight of the Syrian people to the outside world."
The White House said that while it isn't confirming the authenticity of the video itself, it has confirmed that Goto has been murdered. Japan also has deemed the video highly likely to be authentic, said its defense minister, Gen Nakatani.
Highlighted by militant sympathizers on social media sites, the video bore the symbol of the Islamic State group's al-Furqan media arm.
In Jordan late Saturday night, relatives and supporters of al-Kaseasbeh held a candlelit vigil inside a family home in Karak, his hometown in southern Jordan.
We "decided to hold this protest to remind the Jordanian government of the issue of the imprisoned pilot Muath al-Kaseasbeh," said the pilot's brother Jawdat al-Kaseasbeh, holding picture of Muath with a caption: "We are all Muath."
Al-Kaseasbeh's uncle, Yassin Rawashda, said the family just wants to be kept informed.
"We want to know how the negotiations are going ... in a positive direction or not. And we want the family to be (involved) in the course of negotiations," he said.
Jordan and Japan reportedly conducted indirect negotiations with the militants through Iraqi tribal leaders, but late on Friday the Japanese envoy sent to Amman to work on the hostage crisis reported a deadlock in those efforts.
The hostage drama began more than a week ago when the militants threatened to kill Goto and Yukawa in 72 hours unless Japan paid $200 million.
Later, the militants' demand shifted to seeking the release of al-Rishawi, who survived the 2005 attack that killed 60 people when her explosive belt failed to detonate in the worst terror attack in Jordan's history.
The deadline for that exchange passed without word, leaving the families of the pilot and journalist waiting in agony. Al-Rishawi has close family ties to the Iraq branch of Al Qaeda, a precursor of ISIS.
The Associated Press contributed to this report.