Hungary has banned a conference of extremist groups organized by the U.S.-based National Policy Institute, saying the meeting's speakers advocate racist views contrary to the Hungarian constitution.

Interior Minister Sandor Pinter on Monday ordered national police to prevent the conference from taking place and to block any of the expected speakers, "who are well-known for spreading racist views," from entering or staying in Hungary.

Russia's Aleksandr Dugin, a prominent nationalist ideologue, was among the planned speakers.

Pinter also called on organizers to refrain from further action regarding the conference.

On Sunday, Prime Minister Viktor Orban had asked Pinter to ban the gathering by "all legal means," to which Richard Spencer, director of the National Policy Institute, responded in a statement saying that the event would go on as planned.