Tokyo - The clock was ticking on Thursday towards a deadline imposed by Islamist militants threatening to kill two Japanese nationals unless Tokyo pays a $200m ransom.The Japanese government said it was working to secure the release of freelance journalist Kenji Goto and self-employed contractor Haruna Yukawa, but with only 24 hours to go, admitted it had still not spoken to ISIS."We have not been able to confirm their safety," chief cabinet secretary Yoshihide Suga told a press conference.Jihadist footage posted online on Tuesday showed a knife-wielding militant looming over two kneeling Japanese men, apparently in a desert in Syria or Iraq.In a chilling echo of the group's videotaped beheadings of five western hostages last year, the man, who speaks English with a British accent, says the two captives' fate hangs in the balance."You now have 72 hours to pressure your government into making a wise decision by paying the $200m to save the lives of your citizens," he says.Tokyo believes the deadline will expire at 14:50 on Friday.The Islamists have linked the ransom to the amount of cash Prime Minister Shinzo Abe said he would be earmarking to help countries dealing with an influx of refugees fleeing fighting between IS and regular forces.The black-clad figure said the money amounted to fighting against IS.Part of Japan's strategy in dealing with the crisis appears to be regularly stressing the non-military, humanitarian nature of this aid."They are totally wrong about our position," Suga told journalists."We wish not to fight against the world of Islam, we want to help the more than ten million refugees in the region. This is humanitarian and non-military support. We want them to understand this, and free the hostages immediately."Doctored imagesThere have been a variety of public reactions in Japan to the unfolding drama, with some of Abe's domestic opponents tying it to his more assertive foreign policy drive and saying it highlights the risk of his brand of international engagement.Among the general public there is a sense of bafflement, reflected in pieces in newspapers and on television seeking to answer the question: "Why Japan?".Meanwhile, social media has seen an eruption of doctored images in which the picture of the armed militant looming over two kneeling men is altered -- one montage replaces the knife he wields with a banana, while others play on video game themes.A supportive narrative was building around Goto, a respected and experienced war reporter whose work has sought to highlight the plight of children in conflict zones.In video footage he filmed around the time he entered Syria, he holds identification papers and his Japanese passport and explains that he is aware of the risks."Whatever happens, I am the one who is responsible," he says. "I am asking you, Japanese people, do not place responsibility on the people of Syria. Please. I am sure I will come back alive, though."Ko Nakata, Islamic law scholar and visiting professor of Doshisha University, who also goes by the name Hassan, told reporters he was happy to mediate in talks between the Japanese government and the jihadists.Nakata, whose home was raided by police in October over suspicions he was in league with militants, said an ISIS commander contacted him in September to suggest he could save Yukawa's life by participating a "trial" under Islamic law.However, because of the police probe, he was now unable to communicate with the commander, he said."But with this press conference I hope my message will reach the international community including the Japanese government," Nakata said.He also addressed a message in Arabic to his "old friends" in the Muslim world, pleading for an extension to the 72-hour deadline.The ISIS group has previously killed three Americans and two Britons after parading them on video, but this is the first time Japanese citizens have been threatened, and the first time a ransom demand has been made.