Police believe they have tracked down the prankster responsible for sending e-mail to subscribers of NTT DoCoMo's i-mode mobile phone service that causes the phones to automatically dial the police, investigative sources said Thursday.

They said police identified the man, a resident of northeastern Japan, by analyzing the communication records of DoCoMo and a Tokyo-based Internet service provider to which the man subscribes.

The Tokyo Metropolitan Police Department and the Kochi Prefectural Police Department began looking into the case after police forces in Tokyo and Kochi noted that their 110 emergency police phone systems were flooded with phony calls starting in late May.

Police investigators are questioning the suspect on a voluntary basis.

The e-mail invites users of the Internet-capable phones to access a Web site by clicking on an image of a bomb. If the user does so, the phone automatically dials the police.

Kochi Prefectural Police received up to 100 false calls triggered by the e-mail a day between late May and early June, against an average of 250 genuine calls a day.

The emergency phone system at the Metropolitan Police Department was also affected by prank e-mail, but sources said the department has difficulty tracking the exact number because about 1,200 prank or mistaken calls come in each day.

The number of subscribers to the i-mode service totaled 10.02 million by Sunday, topping the 10 million mark 17 months after the service was launched, the mobile phone operator said Monday.

The service enables users to send and receive e-mail and access modified Web sites on their handsets.