An official admitted the government had "concerns" about the speech by Ejovi Nuwere, a Boston-based consultant, which was scheduled at an international security symposium in Tokyo last November.

Nuwere filed a civil case alleging violation of freedom of expression. He accused the internal affairs ministry of pressuring conference organizers to cancel his speech.

"It was my impression that they felt if I said 'This is how we can improve the system', that means that the system needs to be improved. And they refused to admit that," Nuwere told a press conference.

Nuwere was due to speak about Juki-Net, a computer network launched in 2002 in which municipalities assign identification codes to residents to let government agencies track people by name, gender, address and date of birth.

Nuwere said he had discovered "several fundamental flaws" in the system but had not planned to detail them in his speech. He had been under contract to work with the central prefecture of Nagano, which opposed Juki-Net.

Many mayors, computer experts and privacy activists wanted to stop Juki-Net, saying personal data could be leaked due to technical glitches or computer illiteracy by local officials.

The internal affairs ministry runs the project and was an official supporter of the symposium.

"There were concerns that the planned speech would lead to disclosure of particular vulnerabilities of particular systems, like talking about how to open locks on certain doors," a ministry official in charge of information security told AFP.

He said the ministry spoke with symposium leaders but denied that it tried to suppress freedom of speech.

"We welcome all sorts of opinions being expressed about Juki-Net. That's not a problem. But a person who penetrated certain systems was going to talk about his experience at the symposium. We had concerns," he said.

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