Japan reacted with shock and anger Sunday after an online video was released that appeared to show Islamic State executing Japanese journalist Kenji Goto -- the apparent end to a frantic past couple of days in which officials tried negotiating to save Goto’s life.

The video, called "A Message to the Government of Japan," featured a militant who looked and sounded like a militant with a British accent who has taken part in other beheading videos by the Islamic State group. 

Goto, kneeling in an orange prison jumpsuit, said nothing in the roughly one-minute-long video.

"Abe," the militant says in the video, referring to the Japanese prime minister, "because of your reckless decision to take part in an unwinnable war, this knife will not only slaughter Kenji, but will also carry on and cause carnage wherever your people are found. So let the nightmare for Japan begin."

Japanese Prime Minister Shinzo Abe expressed outrage at the video that was released on militant websites.

"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 without words," he said. "The government has been doing its utmost in responding to win his release, and we are filled with deep regrets."

He vowed that Japan will not give in to terrorism and will continue to provide humanitarian aid to countries fighting the Islamic State extremists.

The country was mourning a man who according to friends and family braved hardship and peril to convey through his work the plight of refugees, children and other victims of war and poverty.

"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 Keji might be able to come home," said Goto's brother, Junichi Goto. "I was hoping he would return and thank everyone for his rescue, but that's impossible, and I'm bitterly disappointed."

Ishido earlier told NHK TV her son's death showed he was a kind, gentle man, trying to save another hostage. That hostage, Haruna Yukawa, was shown as purportedly killed in an earlier video.

The White House released a statement late Saturday condemning what it called q "heinous murder."

"Our thoughts are with Mr. Goto’s family and loved ones, and we stand today in solidarity with Prime Minister Abe and the Japanese people in denouncing this barbaric act," the statement said. 

The White House’s National Security Council issued a statement minutes after the release of the video stating intelligence officials are, as with similar recent videos, trying to verify its authenticity.

The hostage drama began last week after Islamic State threatened to kill Goto and fellow Japanese hostage Haruna Yukawa in 72 hours unless Japan paid $200 million.

A purported militant message released Jan. 24 claimed Yukawa had been killed.

The militants later demanded the release of Sajida al-Rishawi, who is on death row in Jordan for her role in a 2005 al Qaeda attack on hotels in Amman that killed 60 people.

Within hours, the militant group said it instead wanted al-Rishawi, 44, released in exchange for the life of hostage Lt. Muath al-Kaseasbeh, a Jordanian fighter pilot.

Late Friday, after the deadline for a deal had passed, Japan's deputy foreign minister, Yasuhide Nakayama, said that efforts to free Goto were "in a state of deadlock."

The 26-year-old al Kaseasbeh's plane went down in December over an Islamic State-controlled area of northeastern Syria.

He is the first foreign pilot to be captured by the group since a U.S.-led military coalition began carrying out airstrikes against the extremists in September. Jordan is part of the coalition.

Kaseasbeh's family said late Friday there has been no word about the 26-year-old pilot’s fate.

Goto was captured in October, after he traveled to Syria to try to win the release of Yukawa.

Jordan and Japan are reportedly conducting indirect negotiations with the militants through Iraqi tribal leaders.

The Associated Press contributed to this report.