Investigators arrested 13 people Wednesday and raided several locations nationwide in connection with extortion activities targeting users of a telephone chat service in more than 30 prefectures, police sources said.

Altogether, hundreds of millions of yen may have been swindled through the operation, they said.

Those arrested by a joint Miyagi, Aichi and Gifu prefectural police team include company employees Nobuyuki Kankawa, 26, Megumi Gen, 25, and Mikiko Monma, 23, all from Tokyo, as well as three unnamed juveniles. All are being held on suspicion of fraud.

Warrants were being prepared for others suspected of belonging to the same group, the sources said. The locations raided included the office of Groovin', a company in Tokyo's Shibuya Ward. Police were also preparing a warrant for the firm's 27-year-old president, whose whereabouts are not known, they said. His name was not released.

The sources alleged that the group contacted at least five users of the phone service, including a 21-year-old man residing in Saitama Prefecture, during the period spanning from late January to early this month and falsely told them their chat-line phone bill payments were in arrears.

The group threatened to bring the case to the attention of "those who would collect such debts through unpleasant means" if the money was not repaid, and swindled the five men out of about 247,000 yen in total, the sources said.

The telephone "chat services" usually provide a medium for men and women to talk with each other without knowing the other's identity.

Police are currently looking into how the group managed to get lists of users of these services and exactly how much money was involved, sources said.