Czech police detained former Ku Klux Klan leader David Duke in Prague on Friday on suspicion of supporting or denying the Holocaust, the Czech news agency CTK reported.
Duke arrived in Prague earlier this week at the invitation of local neo-Nazis to publicize the Czech translation of his 1998 memoir My Awakening.
A police spokesman told CTK that Duke was being questioned by police.
Police have detained Duke for claims in his book that the systematic mass murder of Jews and other ethnic groups by Nazi Germany during World War II never took place, a hate crime in the Czech Republic punishable by up to three years in prison, according to police spokesman Jan Mikulovsky.
Duke was planning to give talks in the capital as well as in the country's second largest city of Brno.
Earlier this week Prague's Charles University banned Duke for giving a lecture on extremism. The university said it canceled the talk out of a fear that it could have been attended by neo-Nazis.
Political activities of Czech far-right groups have been on a rise in recent months, including provocative marches through Roma ghettos in troubled Czech towns.
There was no information whether they would charge Duke, who is a former U.S. presidential contender and advocates racial separation.