Islamic State militants have beheaded captive Japanese journalist Kenji Goto, after Tokyo’s negotiations with IS reached a “deadlock.” The gruesome video of the execution appears to be genuine, Japan said, vowing justice for those responsible.

The horrifying video shows a hooded man standing over another man – apparently Goto – with a knife held to his throat. It then shows footage of a body with a head placed on it.

Japanese Defense Minister Gen Nakatani said the video appears to be genuine. The comment comes after a meeting of ministers, where Tokyo police representatives said the footage had a “high degree of credibility.”

Earlier on Saturday, Yasuhide Nakayama – the head of Tokyo’s emergency response team in the Jordanian capital of Amman – told journalists that there had been no progress in attempts to negotiate the release of Goto and Maaz al-Kassasbeh, a first lieutenant in the Jordanian Air Force.

In the clip, the man – who calls himself Jihadist John and speaks in English with a British accent – addresses the Japanese government, blaming Tokyo for the slaughter. He said that Japan started an “unwinnable war,” and threatened its government with more violence.

Japanese Prime Minister Shinzo Abe has condemned the “inhumane and contemptible act of terrorism,” promising to “never forgive these terrorists.”

"Japan will work with the international community to bring those responsible for this crime to justice," Abe added in brief statement to journalists.

Chief Cabinet Secretary Yoshihide Suga has also condemned the atrocity, saying he "cannot help feeling strong indignation that an inhuman and despicable act of terrorism like this has been committed again."

Jordan on Sunday condemned the killing of Goto. The IS demanded the release of a female terrorist from a Jordanian prison in exchange for the hostage. Jordan was involved in negotiations with the jihadists.

"The Jordanian government strongly condemns the execution of the second Japanese hostage by the terrorist organisation Daesh," Jordan's government spokesman told state media, using a pejorative Arabic acronym for the group.

The government in Amman reiterated that it was still offering to swap a Jordanian pilot for an Iraqi prisoner connected to the Islamic State.

Meanwhile, the United States is “standing together with a broad coalition of allies and partners” and will continue taking “decisive action to degrade and ultimately destroy [the Islamic State]," President Obama promised.

"The United States condemns the heinous murder of Japanese citizen," Obama said in a statement released by the White House.

Previously, Tokyo agreed with the militants on an exchange of Goto for Sajida al-Rishawi, the Iraqi woman who killed 60 people in a 2005 Jordan bombing. A Jordanian government spokesman has also said that Amman is prepared to free Rishawi if its pilot is freed in return. Al-Kasasbeh was captured by the Islamic State in late December after his plane came down during an air raid by the US-led coalition.

READ MORE: Japan says won’t pay hostage ransom to ISIS as deadline looms

Goto was captured by IS militants in October 2014 when he returned to Syria to search for his friend, Japanese national Haruna Yukawa. The latter was taken hostage by extremists in August.

On January 20, the militants published a video on several jihadist websites showing the two Asian men wearing orange fatigues and standing on their knees, while a masked man in black holds a knife. In the video, the militant group demands a $200 million ransom to be paid for the hostages' lives within 72 hours – the same amount of money that Japan had pledged to pay to the US-led campaign against IS.

Japanese Prime Minister Shinzo Abe said he will stand by his country’s commitment not to pay ransoms, adding that “this policy is unshakable and we won’t change it.”

As the 72 hours expired, IS released a video where Goto shows a picture of the beheaded body of his fellow captive on January 24. In the message addressed to the Japanese government, Goto said that the jihadist group now wants the release of Iraqi suicide bomber Rishawi.