TOKYO (Reuters) - Japan's government opened a communication channel with Islamic State in Iraq and Syria (ISIS) in the decisive stages of its recent hostage crisis but was unwilling to use it to start negotiations, according to a Tokyo-based Islamic scholar who briefly became an intermediary.

Hassan Ko Nakata, 54, who police suspected was a recruiter for ISIS, was asked by the foreign ministry to pass on a message to the group at the peak of the crisis last month, according to Nakata, associates and records reviewed by Reuters.

The request, which has not been previously revealed, shows Tokyo appeared ready at one point to talk to ISIS to free two Japanese men who had been captured in Syria for ransom, despite the government's public vow not to give in to terrorism.

ISIS beheaded the two hostages - self-styled security consultant Haruna Yukawa and veteran war reporter Kenji Goto - days later after Japan decided to team up with Jordan to deal with the crisis, a move that is now under scrutiny at home.

That decision to work exclusively with Amman, which was also trying to free a Jordanian military pilot held hostage by ISIS, not only closed communications via Nakata but also effectively ended separate contact that had opened up between the wife of Goto, 47, and his captors.

"The government sidelined whatever private communication channels there were in place and proved unable to establish effective contact with the militants until the very end," said Nils Bildt, president of security consultancy CTSS Japan, which has worked for the Japanese government.

Bildt said that may have been a mistake.

The foreign ministry's anti-terrorist taskforce declined to comment on Nakata's specific allegations. "The Japanese government took all possible measures and considered all options to deal with the hostage crisis but I would like to refrain from commenting on specific steps undertaken by the government," said taskforce official Takanori Hayashi.

Nakata, who says he no longer supports ISIS, said he became involved in the hostage crisis last September when he went to Syria on his own accord in a failed bid to secure the release of Yukawa, the first hostage to be taken.

Goto made a similar mission in late October to free Yukawa but ended up a captive himself.

Shortly after, Goto's wife, Rinko, received an email from ISIS representatives and tried to engage in talks with the help of a British security consultancy and people who had worked with Goto in the Middle East, according to four people involved.

Japanese officials had privately told the families of Yukawa and Goto that they would not pay a ransom if asked.

Then late last month, after Nakata's return to Japan from Syria, he said he became an intermediary between the foreign ministry and a person he identified as a Chechen fighter with ISIS, Umar Ghuraba, who was based in northern Syria. "I just wanted to use my connections with the Islamic State to help solve the crisis," Nakata said.

A MESSAGE TO ISLAMIC STATE

A former Islamic law professor at Kyoto-based Doshisha University, Nakata converted to Islam in 1979. He had expressed support for ISIS on Twitter and posed with a gun before the group's flag. He says he does not support ISIS now but maintains friendships with militants.

On Jan. 21, a day after ISIS announced a 72-hour deadline to pay US$200 million (S$250 million) for Goto and Yukawa, officials at Japan's anti-terrorism taskforce sent an email to an associate of Nakata, Shiko Ogata, 31.

The email contained a message addressed to ISIS and a request it be passed on. Email records show Ogata sent it to Nakata.

The message in English and Arabic said: "We strongly urge the group not to harm the two Japanese nationals and to release them immediately." It did not address the ransom demand.

Nakata said he decided not to forward the message, believing it showed no willingness to talk. "If I passed this on, it would be like sending a message to kill the hostages," he said.

The ministry did not follow up with him on the message or the response from ISIS, Nakata added.

But on Jan. 23, as the ransom demand neared, Nakata received a message from Umar via WhatsApp, a smartphone application. It was just after 4:30 in the morning in Tokyo, 9:30 at night in Syria.

"There isn't much time left. The Islamic State will carry out its promise," Umar said in a message in Arabic and translated by Nakata. Umar's identity and his connection to those holding the hostages could not be confirmed.

The militant asked Nakata whether an audio message Umar claimed to have obtained via "negotiation channels" was credible. In it, a man identifies himself as Masayuki Magoshi, a diplomat at Japan's embassy in Jordan. Speaking Japanese, he says Japan is "serious" about securing the hostages and states their names and dates of birth.

Reuters could not verify the recording's authenticity. "It's credible," Nakata wrote back after saying he had called the head of the foreign ministry's anti-terrorism taskforce to confirm the statement in the middle of the night. "It's important that the conditions of the Islamic State are met," Umar wrote back.

The next day a video purportedly showing a beheaded Yukawa was published online. Goto was killed a week later. Nakata says he never heard back from the anti-terrorism taskforce. He says he has not been in touch with Umar since.