Pope Emeritus Benedict XVI made his comments in a letter published by Italy’s La Repubblica newspaper on Tuesday.

Benedict was responding to the book Dear Pope, I Write to You, by Piergiorgio Odifreddi, a member of the Italian Union of Rationalist Atheists and Agnostics.

Odifreddi's 2011 book was his reaction to Benedict’s best-known tome Introduction to Christianity.

In his first public comments since he retired in February, Benedict thanks Odifreddi for his attempts to engage in an open dialogue with the Catholic faith.

The 86-year-old writes of his surprise that Oddifreddi viewed his book so worthy of such detailed discussion, given that he considers theology to be “science fiction”.