Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

TOKYO - Japan promised Saturday not to give up "until the very end" on efforts to free two Japanese hostages threatened with beheading by Islamic militants demanding a $200 million ransom, after a deadline passed with no word from the captors.

Militants affiliated with the Islamic State group posted an online warning Friday afternoon that the "countdown has begun" for the extremists to kill 47-year-old journalist Kenji Goto and 42-year-old adventurer Haruna Yukawa. The extremists had set a 72-hour deadline for Prime Minister Shinzo Abe to pay the ransom, or the hostages would be killed, in an online video posted Tuesday.

Friday's posting, which appeared on a forum popular among Islamic State militants and sympathizers, did not show any images of the hostages, who are believed to be held somewhere in Syria.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Yasuhide Nakayama, a deputy foreign minister sent to Amman, Jordan, said he was working around the clock to coordinate efforts to save the hostages.

"We will not rule out any possibility, and we are verifying all information thoroughly," he said. "We will not give up. I believe it is my duty to ensure we will definitely get them back home, and I will do my utmost to do so."

Yet, the fate of the two men remained unclear Saturday. Top government spokesman Yoshihide Suga said Japan was analyzing the second message.

"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 with the captors.

IN-DEPTH

- The Associated Press