The United Nations' top expert on freedom of opinion and expression expressed concerns about a "distorted media environment" in Hungary, saying on Monday that reporting around elections due next year must be fair and impartial.

UN Special Rapporteur Irene Khan also told reporters during a visit to Budapest that the "freedom of expression which political candidates have should not be abused to create a toxic environment of violence (and) hatred".

Allies of Prime Minister Viktor Orban's Fidesz party control large parts of Hungary's private media, while the public media largely serves as a government mouthpiece. Dozens of newspapers and broadcasters that had criticised Orban have changed hands in recent years.

His government has repeatedly denied undermining press freedom. It did not respond to emailed Reuters questions on Monday.