Atheist's challenge prompts Benedict XVI to break self-imposed silence

Emeritus Pope Benedict XVI has emerged from his self-imposed silence inside the Vatican walls to publish a lengthy letter to one of Italy's best-known atheists.

In it, he denies having covered up for sexually abusive priests and discusses everything from evolution to the figure of Jesus Christ.

Excerpts of the letter were published on Tuesday by La Repubblica, the same newspaper which just two weeks ago published a similar letter from Pope Francis to its own atheist publisher.

Benedict wrote the letter to Piergiorgio Odifreddi, an Italian atheist and mathematician who in 2011 wrote a book Dear Pope, I'm Writing to You. The book was Odifreddi's reaction to Benedict's Introduction to Christianity, perhaps his best-known work.

In his book, Odifreddi posed a series of polemical arguments about the Catholic faith, including the church's sex abuse scandal.

The former Cardinal Joseph Ratzinger headed the Vatican office responsible for abuse cases, and was pope when scandal erupted in 2010, with thousands of people coming forward in Europe, Latin America and beyond saying they had been molested by priests while the Vatican turned a blind eye.