"We are exploring every possibility available to save their lives," Suga said at a press conference, as quoted by Kyodo.
On Tuesday, the Islamic State posted a video showing two Japanese men, Haruna Yukawa and Kenji Goto, allegedly captured by IS militants in 2014 in Syria, kneeling on either side of a man clad in black fabric from head to toe and holding a weapon. An English-language voiceover states that the two men will be killed unless the Japanese government pays a $200-million ransom.
The sum matches exactly the amount pledged to the anti-IS coalition by Japanese Prime Minister Shinzo Abe on Saturday during his Middle East tour. Tokyo has stressed that Abe's monetary pledge to the coalition is strictly for humanitarian and non-military purposes.
The deadline for paying the ransom is Friday (05:50 GMT), according to Japanese authorities.
The Islamic State is a jihadist group known for multiple human rights atrocities, including beheading of journalists, aid workers and civilians, some of which are documented in video and posted to the Internet. In 2014 IS took large areas of Iraq and Syria under its control and proclaimed a caliphate.