TOKYO (AFP) - Japan said Wednesday it was asking the Jordanian government for help after the Islamic State in Iraq and Syria (ISIS) extremist group released a new video threatening to kill a captured Japanese journalist within 24 hours.

"The government in this extremely difficult situation has been asking for assistance from the Jordanian government towards securing (Kenji) Goto's early release," Chief Cabinet Secretary Yoshihide Suga told reporters.

The militants are demanding the release of an Iraqi woman convicted for her part in multiple bombings in Amman in 2005 that killed 60 people in exchange for Goto.

Suga said in the wake of the video's release Tuesday, senior officials had held an emergency meeting in Tokyo.

"We confirmed that Japan's policy (of seeking assistance from Amman) remains unchanged.

"With the prime minister's approval, I told the foreign minister to convey the prime minister's instructions to (the government's representatives in Jordan)".

Suga was speaking at an impromptu press conference around 1am (midnight Singapore time) after news broke of the new video purportedly from the Islamic State in Iraq and Syria group.

Goto was snatched by militants in October last year after venturing into Syria on a mercy mission to free his friend Haruna Yukawa.

Yukawa was apparently executed last week after Japan failed to meet an initial US$200 million (S$270 million) ransom demand by Friday.

Friends of Goto told national broadcaster NHK things were grave.

"The situation is turning extremely difficult," said freelance journalist Kosuke Tsuneoka.

"I believe people thought a negotiation might be possible. Perhaps negotiations are ongoing, but they are applying further pressure."

Fellow journalist Takeharu Watai told the broadcaster the 24 hour time limit made action urgent.

"The least we can do is to ask for more time and extend the deadline," he said.