A U.N. rights expert who visited Japan last year noted "significant worrying signals" for the country's freedom of expression and opinion in a report released Tuesday in Geneva.

The lack of debate over historical events, restrictions on access to information justified on national security grounds and government pressure on media "require attention lest they undermine Japan's democratic foundations," said David Kaye, U.N. special rapporteur on the right to freedom of opinion and expression.

The report, to be presented to the U.N. Human Rights Council in June, is the result of the first research ever on freedom of expression in Japan conducted by a U.N. special rapporteur.