AMSTERDAM, Netherlands, May 16 (UPI) -- A Dutch cartoonist has been arrested following a lengthy investigation into allegations his work was discriminatory to other races, authorities say.

Radio Netherlands said Friday that the artist, who works under the pseudonym Gregorius Nekschot, was arrested and had a number of his materials seized as part of the ongoing investigation.

The investigation into Nekschot, who has kept his identity hidden since 2005, was initially brought about after an imam complained about the artist's works.

The imam alleged the works were insulting and discriminatory against both Muslims and individuals of other races, Radio Netherlands said.

The radio report said while Nekschot was released one day after Tuesday's arrest, Parliamentary Member Boris van der Ham has questioned why the cartoonist was arrested for his "extremely controversial" works.