TOKYO - Japan was scrambling Sunday to verify a video posted online claiming that one of two men held hostage by Islamic State jihadists had been executed, as Prime Minister Shinzo Abe condemned the militant’s “intolerable violence”.

Abe called an emergency meeting of senior ministers that began at around 1.20am (1620 GMT Saturday) as his government demanded “the remaining” hostage be immediately set free. “A photograph apparently showing Mr Yukawa had been murdered has been posted on the Internet,” Abe said.

“The pain the family is feeling must be beyond what we imagine. This is an act of terrorism and intolerable violence.

“I am infuriated. I condemn it absolutely. Again I strongly demand they not harm Mr Goto and release him.”

“The images show Kenji Goto holding a photo of Haruna Yukawa apparently dead has been posted on the internet,” Abe’s chief spokesman Yoshihide Suga told a press conference shortly after midnight.

The government is currently working to confirm the authenticity of the video, added defence chief Gen Nakatani.

The video was not posted on any of the IS group’s official channels and it does not bear the group’s black and white flag. The purported execution of Yukawa is also not shown.

Several supporters of the IS group on social media channels have contested the veracity of the video, while Rami Abdel Rahman, director of the Syrian Observatory for Human Rights, said negotiations for the two men’s release are still ongoing.

“We have seen the video purporting to show that Japanese citizen Haruna Yukawa has been murdered by the terrorist group ISIL. The intelligence community is working to confirm its authenticity,” the US National Security Council deputy spokesman Patrick Ventrell said in a statement, using alternative acronyms for the militant group.

If Yukawa’s death is confirmed, it would mark a very grave turn of events for Japan, which has been on edge since the Islamic State group released a video on Tuesday demanding a $200 million ransom within 72 hours.

There had been no news of the fate of freelance journalist Goto or self-employed contractor Yukawa since the deadline expired at 0550 GMT on Friday.

The jihadist group, which rules large swathes of Iraq and Syria under a strict form of Islamic law, has murdered five Western hostages since August last year but this is the first time it has threatened Japanese captives.

Junko Ishido, Goto’s mother, on Friday launched an emotional appeal begging for mercy for her son.

“I say to you people of the Islamic State, Kenji is not your enemy. Please release him,” she said.

Japanese officials have repeatedly said they are trying to make contact through various channels.

Yosuke Isozaki, an advisor to Prime Minister Shinzo Abe, on Friday reportedly said there had been some “indirect” communication with the militants, but “nothing direct”.

Tokyo has little diplomatic leverage in the Middle East, but local media say Abe may try to use his close relationship with Turkey’s President Recep Tayyip Erdogan to rescue the hostages.

Japan’s Yomiuri Shimbun newspaper reported Saturday that Jordan has also tried to contact the Islamic State through influential religious leaders in Amman.

The Islamists linked their $200 million ransom demand to the amount Abe said he would earmark to help countries dealing with the influx of refugees fleeing fighting between IS militants and regular forces.

Tokyo is under pressure from Britain and the United States to stand firm on the group’s cash demands, as both countries have a policy of never paying ransoms.

Broadcaster NHK on Friday quoted a “public relations” official from the Islamic State group describing the Japanese as “infidels” for supporting efforts to stop them.

The Japanese media has rallied around Goto, a respected and experienced war reporter whose work has appeared on domestic television channels.

In video footage he filmed around the time he entered Syria, he holds identification papers and his Japanese passport and explains that he is aware of the risks.

“Whatever happens, I am the one who is responsible,” he says. “I am asking you, Japanese people, do not place responsibility on the people of Syria. Please. I am sure I will come back alive though.”