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.