The posting which appeared today shows a clock counting down to zero along with gruesome images of other hostages who have been beheaded by the Islamic State group.
The militant group gave Japanese Prime Minister Shinzo Abe a 72-hour deadline which expired today to pay a USD 200 million ransom for the two hostages. The posting on a forum popular among Islamic State militants and sympathisers did not show any images of the Japanese hostages.
The status of efforts to free the two men was unclear.
Government spokesman Yoshihide Suga, when asked about the latest message, said Japan was analysing it.
"The situation remains severe but we are doing everything we can to win the release of the two Japanese hostages," Suga said. He said Japan is using every channel it can find, including local tribal chiefs, to try to reach the captors.
He said there has been no direct contact from the hostage takers.
"All Muslims in Japan, we want the Japanese hostages to be saved as soon as possible," said Sandar Basara, a worker from Turkey.
Prime Minister Shinzo Abe convened his National Security Council to discuss how to handle the crisis, as the mother of one of the captives appealed for her son's rescue.
"Time is running out. Please, Japanese government, save my son's life," said Junko Ishido, the mother of 47-year-old journalist Kenji Goto.
"My son is not an enemy of the Islamic State," she said in a tearful appearance in Tokyo.
