Militants had threatened to kill Jordanian pilot Muath al-Kasaesbeh unless a would-be suicide bomber being held on death row in Amman was handed over by sunset on Thursday.
Japanese journalist Kenji Goto was also being held by the militants.
“The situation is deadlocked,” Japan’s deputy foreign minister, Yasuhide Nakayama, said in Jordon late on Friday according to Japanese public broadcaster NHK.
Foreign Minister Fumio Kishida said in Tokyo on Saturday that the situation was unpredictable and that anything could happen, NHK reported.
“Anything could happen,” he said. “We can’t predict it at all. While preparing for every situation, I want to make every effort for Mr. Goto’s release.”
Chief Cabinet Secretary Yoshihide Suga arrived at the Prime Minister Shinzo Abe’s office on Saturday afternoon, and the prime minister is on standby to receive regular updates on the situation, NHK said.
Jordan’s army said on Friday state agencies were “working round the clock”.
An audio message purportedly from Goto said the pilot would be killed if Jordan did not free Sajida al-Rishawi, jailed for her role in a 2005 suicide bomb attack that killed 60 people in Amman.
The message extended a previous deadline set on Tuesday in which Goto said he would be killed within 24 hours if al-Rishawi was not freed.
The hostage crisis comes as Islamic State, which has already released videos showing the beheadings of five Western hostages, is coming under increased military pressure from U.S.-led air strikes and by Kurdish and Iraqi troops pushing to reverse the Islamist group’s territorial gains in Iraq and Syria.
Abe has repeatedly said Japan would not give in to terrorism and would keep cooperating with the international community.
The hostage crisis erupted after Abe announced in Cairo $200 million in non-military aid for countries opposing Islamic State, but his government has rejected suggestions it acted rashly and stressed the assistance was humanitarian.
Goto went to Syria in late October. According to friends and business associates, he was attempting to secure the release of Haruna Yukawa, his friend and fellow Japanese citizen who was captured by Islamic State in August.
In the first video purportedly of Goto, released just over a week ago, a black-clad masked figure with a knife said Goto and Yukawa would be killed within 72 hours if Japan did not pay Islamic State $200 million.
A video last Saturday appeared to show Goto with a picture of a decapitated Yukawa, saying his captors’ demands had switched to the release of al-Rishawi. Tuesday’s video featured an audio track over a still picture that appeared to show Goto holding a picture of Kasaesbeh. (REUTERS)