In an address to librarians and publishers this week, Khamenei warned: "Not all books are necessarily good. … Some books are harmful," his official Web site said.
"Like poisonous, dangerous and addictive drugs which are not available for everyone without restrictions … as a publisher, librarian or an official in the book industry, we don't have the right to make [such books] available to those without knowledge," the top cleric said. "We should provide them with healthy and good books."
Ataollah Mohajerani, a former culture minister now exiled to Britain, told The Guardian newspaper Khamenei spoke "with specific political hidden motives."
"I think that he is very much concerned about books that can either implicitly or explicitly target his position as the supreme leader and also his legitimacy," Mohajerani said.
Khamenei did not single out titles for banning, but works ranging from Plato's Symposium to the writings of James Joyce, Gabriel Garcia Marquez and Kurt Vonnegut have been blocked by the Ministry of Culture and Islamic Guidance.
Iranian writers often complain of long delays in getting approval for publication.