TOKYO, Feb. 1 -- The Islamic State (IS) militant group claimed in a video posted online late Saturday that it had killed a second Japanese hostage, Kenji Goto.

Saturday's IS executition video showed a hooded man stood over Goto, and held a knife to his throat. The following footage showed a head placed on a body.

The Japanese government said on Sunday it was "highly probable" that the authenticity of the video was "highly probable".

"After an extensive review, we believe it's highly probable" the video is real, government spokesman Yoshihide Suga said.

If proven to be true, it means that Japan has failed in rescuing both of its nationals held by the militant group. A week ago, the IS killed 42-year-old contractor Haruna Yukawa, who was believed to be captured last August in the northern Syrian city of Aleppo. His fellow countryman Goto captured in Syria late October during a trip to rescue him.

The lastest IS execution video came a day after Japan said the collective efforts by Japan and Jordan to save the captured Japanese journalist and the Jordanian pilot are "deadlocked" and the situation remains highly unpredictable.

"The situation is deadlocked," Japan's deputy foreign minister, Yasuhide Nakayama, said in Jordon late on Friday, according to Japanese public broadcaster NHK.

The IS earlier proposed a prisoner swap, to exchange Goto and Jordanian pilot Lt. Mu'ath al-Kaseasbeh with a trained suicide bomber jailed for her role in a 2005 attack that killed 60 people in Amman.

Before the execution of the first Japanese hostage, the IS had demanded a ransom of 200 million U.S. dollars from the Japanese government so that the two Japanese nationals could be freed.

The amount of the ransom equaled to that of the assistance Japanese Prime Minister Shinzo Abe promised during his recent tour in Egypt to offer to regional countries in their battles against the IS militants.

Like the slaying of Yukawa by the IS, the purported beheading of Goto, a 47-year-old freelance journalist, has also prompted a wave of condemnation.

UN Secretary-General Ban Ki-moon on Saturday condemned the "barbaric murder". "Once again, the Secretary-General calls for the unconditional release of all hostages held by Daesh and others," said a note released by Ban's spokesperson.

Japanese Prime Minister Shinzo Abe said following the release of the video he was outraged by the IS militant group's alleged murder of Goto and would never forgive terrorists.

U.S. President Barack Obama also condemned the "heinous murder" in a statement released by the White House, vowing to continue "taking decisive action" to degrade and ultimately destroy IS with a broad coalition of partners.

Meanwhile, French President Francois Hollande voiced indignation over the incident, vowing that France and Japan would "continue to work together for peace in the Middle East and to eliminate terrorist groups."