The Islamic State group, in a video message seen on Tuesday, said it would kill the hostages within 72 hours unless it receives USD 200 million. Based on the video's release time, that deadline would come sometime .
Government spokesman Yoshihide Suga said that Japan was trying to reach those holding the hostages, 47-year-old freelance journalist Kenji Goto and 42-year-old Haruna Yukawa, the founder of a private sometime on Friday company.
Suga said Japan had not received any message from IS since the release of the video.

Ko Nakata, an expert on Islamic law and former professor at Kyoto's Doshisha University, told reporters he was able to reach the Islamic State.
He and Kosuke Tsuneoka, a Japanese journalist who was held hostage in Afghanistan in 2010, have both offered to reach out to the Islamic State to try to save the hostages.
"Seventy-two hours is too short a time, and I myself am prepared to go to negotiate," Nakata said, speaking in both Japanese and in Arabic.
He urged the Islamic State group not to harm the hostages, saying releasing them would be a good deed that would improve its image.
Tsuneoka put out a tweet offering to go with Nakata on such a mission, saying that if the Islamic State could guarantee their safety and accept them as negotiators, "we can directly appeal for the release of Mr. Yukawa and Mr. Goto from the Islamic State."
Asked if Japan would consider the offer by Tsuneoka and Nakata to intercede, Suga said Tokyo was "prepared to consider all possible ways to save the two hostages."
It is unclear whether the two private citizens would be able to contact and negotiate with the Islamic State group even if they were to travel to Syria. Japan lacks any diplomatic presence in Syria.
Prime Minister Shinzo Abe, who returned from a six-day Middle East tour on Wednesday, vowed not to give in to terrorism, and to continue to cooperate on providing humanitarian aid to those affected by conflict in the region.

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