Japan is vowing to "never give up" its struggle to save two hostages held captive by Islamic State militants.

Whether freelance journalist Kenji Goto and Haruna Yukawa, the self-employed contractor he had gone to rescue, are alive remains unknown a day after the expiry of a deadline to secure their release and no word from their captors.

The Islamist militants had threatened on Tuesday afternoon to kill the hostages if they did not receive $US200 million ($A248.23 million) in 72 hours.

Deputy Foreign Minister Yasuhide Nakayama, who was heading Japan's efforts to rescue its two nationals out of Jordan's capital Amman, told reporters on Saturday: "It is a very difficult path to see their release, despite a variety of routes.

"We are focusing on scrutinising information over again. We will never give up. We will bring them home."

Foreign Minister Fumio Kishida said there was "nothing new to report" after a meeting of an emergency taskforce.

Islamic State militants released a video this week in which Goto and Yukawa, apparently kneeling in the desert, are threatened with execution by a man with a British accent.

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 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.

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

Japanese officials said they are still trying secure a channel of communication to contact the Islamic State group as they scrutinise various information.

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