The wife of Kenji Goto, identified Wednesday as one of the two Japanese hostages held by the Islamic State group, received an email on her mobile phone in December demanding a ransom of more than ¥2 billion, government sources said Wednesday.

The freelance journalist’s wife first received an email in November from an unidentified party saying that it had captured Goto, according to the sources. His wife exchanged several emails with the party, but the messages did not include threats to kill Goto.

The sources said the government believes the emails were from the Islamic State group, since the address the messages were sent from resembles one used by the group in past hostage cases.

The government officially identified the two hostages shown in a video footage purportedly released by the extremist group as Goto and Haruna Yukawa, a self-proclaimed private security contractor. The group has threatened to execute the two unless Japan pays a $100 million ransom for each.

Goto had headed to the northern Syrian city of Aleppo last October to look for Yukawa, who was reportedly captured by a local armed group in August, a Syrian guide said.

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The 33-year-old Syrian man told Kyodo News on Tuesday that Goto had entered Syria from Kilis, at the southern border with Turkey, and asked the man to accompany him to the northern Syrian city of Raqqa, the militant’s stronghold and de facto capital. But the man refused, saying the area was too dangerous. He said Goto left on Oct. 25 with another man who said claimed to be knowledgeable about the Islamic State group.

According to the guide, Goto took a video of himself on the morning of that day and with messages noting in Japanese and English that he was entering an extremely dangerous area of his own volition, and that no matter what happened, he would come back alive.

Goto also apparently told the guide that he was planning on confronting the extremists over their actions harming innocent Syrians, the man said.

The guide said Goto gave him the telephone numbers of his wife and colleagues and asked him to call them if he didn’t hear from the journalist after a week.

Since the guide was unable to contact Goto after that, he called the man who was accompanying the journalist. The guide said the man told him that Goto had been captured by the Islamic State group in Raqqa and taken to Mosul in northern Iraq. The guide added that he had not been able to contact the man since mid-December.

Goto is said to have met Yukawa last April or May in northern Syria, when the contractor was temporarily held and questioned by the rebel Free Syrian Army, which is fighting to overthrow President Bashar Assad. Goto helped free Yukawa and the two had been in contact since.

In Tokyo, the government was rushing to rescue the hostages before the 72-hour time limit designated by the group expired — but remained unclear of the exact deadline.

The Foreign Ministry obtained the video showing a man wearing a black mask and speaking British-accented English, standing over Goto and Yukawa at 2:45 p.m. Japan time Tuesday. Japan is seven hours ahead of Syria, their presumed location, which means it was 7:45 a.m. Syria time when the ministry learned of the threat.

Government sources, however, say that although Japan has been ordered to pay the ransom within 72 hours, the time limit has not been clearly specified.

Government officials speculate that if the Islamic State group is demanding that Tokyo pay within 72 hours of the government accessing the video, they will have until Friday afternoon in Japan, or Friday morning Syria time, to pay the ransom.

The officials fear that the countdown may have begun when the video was created, in which case significantly less time would be left over.

The video’s authenticity has also been thrown into question, as the hostage crisis spurred speculation the footage might be a video montage. The officials indicated that if the video was fake, it would mean the footage had been created long before its release.

The video, in which an Islamic State militant makes the group’s first public demand for ransom, was posted on extremist websites associated with the group’s al-Furqan media arm.

“We need to rush as we don’t know how much time is left,” a government official said. “The only thing we can do right now is to gather and confirm all available information.”