ISIL says it has killed Japanese hostage Kenji Goto

Islamic State of Iraq and the Levant (ISIL) released a video on Saturday which purported to show the beheading of Japanese journalist Kenji Goto, whom the group has been holding hostage.

The video could not immediately be verified. It showed a hooded man standing over Goto with a knife held to his throat, followed by footage of a body with a head placed on it. Japanese broadcaster NHK said Japan's government was trying to authenticate the video.

The White House said it was working to confirm the video's authenticity. "We have seen the video purporting to show that Japanese citizen Kenji Goto has been murdered by the terrorist group ISIL. We are working to confirm its authenticity,” said National Security Council spokeswoman Bernadette Meehan.

“The United States strongly condemns ISIL’s actions, and we call for the immediate release of all remaining hostages,” she added.

Addressing Japanese Prime Minister Shinzo Abe, the fighter in the video said: "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."

The fighter had the same British accent as the man featured in previous ISIL videos showing beheadings. Goto wore an orange jumpsuit like ISIL captives in past footage. The landscape in the video showed a hill and land covered in scrub, and appeared different from the desert setting of previous videos.

The video follows the passing of a Thursday deadline set by ISIL for the release of Sajida al-Rishawi, who was convicted of involvement in the 2005 bombings of three hotels in the Jordanian capital of Amman in an attack that killed 57 people. ISIL was holding as hostages Goto and Jordanian pilot Moaz al-Kassasbeh, and it offered to release Goto and spare the pilot's life if Jordan released Rishawi.

The video of Goto's purported beheading makes no mention of the Jordanian pilot.

Goto's wife, Rinko Jogo, made a desperate plea for her husband's life on Thursday and revealed that she had exchanged emails with his captors. "In the past 20 hours, the kidnappers have sent me what appears to be their latest and final demand," she said. Goto’s captors told her that if Rishawi was not released by the sunset deadline, "the Jordanian pilot will be executed immediately," Rinko Goto said. "I beg the Jordanian and Japanese government to understand that the fates of both men are in their hands," she wrote.

ISIL is also holding British photojournalist John Cantlie and an American woman captured last year in Syria while working for aid groups. U.S. officials have asked that the woman not be identified out of fears for her safety.

ISIL has suffered recent losses in airstrikes by a U.S.-led coalition. With global oil prices down sharply, its revenue from oil in the territory it controls in Iraq and Syria has likely dropped. The group, which holds a wide stretch of territory in Iraq and Syria after months of intense fighting, is also funding its operations through extortion, human trafficking, and other criminal activities.

Al Jazeera and wire services