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The Islamist terror group ISIS claims it has beheaded a Japanese journalist, a week after beheading another Japanese hostage and demanding the release of a would-be suicide bomber.

A video released Saturday claimed that reporter Kenji Goto was executed after a Thursday deadline for Jordan to release prisoner Sajida al-Rishawi was not met. The tape appears consistent with other ISIS hostage videos, according to Flashpoint Intelligence, a global security firm and NBC News consultant.

Japanese Prime Minister Shinzo Abe condemned the apparent murder, which was the second Japanese citizen the group has claimed to have executed, and vowed that, "Japan will never succumb to terrorism."

"The government has done everything in its power, but I cannot but feel the deepest regret," Abe said at an emergency cabinet meeting Sunday local time. "I am extremely angered by this immoral and despicable act or terrorism. I cannot help but feel extreme regret by the result. We will never forgive the terrorists."

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ISIS had threatened to execute Goto and Jordanian pilot 1st Lt. Mu'ath al-Kasaesbeh if al-Rishawi was not freed within 24 hours. She was on death row in Jordan after her explosives failed to detonate during a 2005 attack on a hotel in the capital of Amman.

Jordan demanded proof of life of the two captives, while Japan's Deputy Foreign Minister Yasuhide Nakayama told reporters Saturday that the situation was “a stalemate.”

ISIS initially demanded a ransom of $200 million for the release of Goto and fellow Japanese captive Haruna Yukawa. Goto had apparently ventured into Syria to rescue Yukawa, who was taken hostage last summer. However, ISIS released a video on Jan. 24 claiming it had beheaded Yukawa and demanding al-Rishawi's release instead.

ISIS later said they would also execute al-Kaseasbeh if al-Rishawi was not freed. Al-Kasaesbeh has been held by ISIS since his fighter jet crashed in Syria in December. ISIS made no mention of the pilot in Saturday’s video.

Japanese broadcaster NHK read a statement Sunday from Goto's mother, Junko Ishido, after the new video was released. "Right now I am too shaken up and in no condition to choose the right words," the statement read. "He went to save his fellow countryman. Please understand his bravery and kindness".

Both Japanese and U.S. officials said they were working to authenticate the tape. Abe vowed to increase Japan’s humanitarian assistance to the Middle East and said, "Japan will resolutely fulfill its responsibility by uniting with the global effort to fight terrorism."

Japan's Chief Cabinet Secretary Yoshihide Suga told reporters that "We cannot suppress the extreme anger that such an immoral and despicable terrorist act was repeated again. Again, we condemn this act,"

President Barack Obama said in a statement that "The United States condemns the heinous murder of Japanese citizen and journalist Kenji Goto."

"Through his reporting, Mr. Goto courageously sought to convey the plight of the Syrian people to the outside world," Obama said. "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."