The fate of two Japanese hostages held by the Islamist terror group ISIS was unclear on Friday after a deadline to pay ransom for their release passed.

Japanese Prime Minister Shinzo Abe previously said saving the men's lives was paramount but his country would not bow to terrorism, Reuters reported A spokesman for his administratio said the government is analyzing developments now that ISIS' deadline had passed.

"The situation remains severe, but we are doing everything we can to win the release of the two Japanese hostages," Yoshihide Suga, the spokesman, told The Associated Press.

Suga said Japan is using a number of channels, including contacts with local tribal chiefs, to try to reach the men's captors.

According to Reuters, ISIS, which calls itself the "Islamic State" and controls large swaths of land in Iraq and Syria, had demanded $200 million to free 42-year-old Haruna Yukawa and 47-year-old Kenji Goto, whom militants had captured in August and October, respectively.

In an online video shared Tuesday, the terror organization gave the Japanese government 72 hours to provide the ransom. A black-clad figure holding a knife stood between the men threatening to kill them if Tokyo refused payment.

Yukawa intended to become a military contractor and was taken in August outside the city of Aleppo, of critical strategic importance in the Syrian civil war between ISIS, moderate rebels and forces loyal to dictator Bashar al-Assad.

Goto, a war correspondent with experience in the Middle East, meanwhile, had traveled to the region in an effort to secure Yukawa's release, only to be captured himself.

"My son Kenji is not an enemy of the people of the Islamic faith," Goto's mother, Junko Ishido, said at a news conference. "He only went to rescue his friend. He has always looked out for weaker people, he was always helping weaker children than him. If I could offer my life, I would plead that my son be released. It would be a small sacrifice on my part."

In 1977, Japan paid $6 million to Japanese Red Army hijackers in Dhaka, Bangladesh, but Tokyo hardened its stance after the 1996 hostage at the Japanese ambassador's residence in Lima, Peru, an incident in which it refused to pay ransom.