BUDAPEST (Reuters) - An 81-year-old German far-right activist has been arrested in Hungary on a European warrant for offences committed while serving a prison term for denying the Holocaust, Hungarian police said on Tuesday.

Horst Mahler, once a founding member of Germany’s leftist Red Army Faction guerrilla group in the 1960s before veering to the ultra-nationalist right, was detained in Sopron near Hungary’s border with Austria, on Monday, police said.

The Budapest chief prosecutor said in a separate statement that based on the European warrant Mahler’s arrest was “justified”. Hungarian officials made no further comment.

German media reported in April that Mahler had left the country to avoid a new prison term for writing far-right tracts while serving a previous sentence for inciting racial hatred and denying Nazi Germany’s Holocaust against Jews.

Mahler was sentenced to 10 years in prison in 2009 on those charges but freed on health grounds in 2015.

He became a far-right activist in later life and joined Germany’s fringe neo-Nazi National Democratic Party.