Pope emeritus Benedict XVI wants his name to be removed from a book on priestly celibacy seen by some Catholics as an attempt to undermine Pope Francis. 

From the Depths of Our Hearts: Priesthood, Celibacy and the Crisis of the Catholic Church is billed by publishers Ignatius Press as being co-authored by the retired Pope and Cardinal Robert Sarah. 

Excerpts of the book drew a strong reaction from Catholics when they appeared in French newspaper Le Figaro ahead of its release today and sparked a row over the exact nature of Benedict's involvement. 

Benedict's personal secretary, Archbishop Georg Gänswein, requested that his name be removed as co-author and that his picture be taken off the front cover. 

The Archbishop claimed that there had been a "misunderstanding" and that while Benedict had indeed sent the cardinal an essay on priestly celibacy, he had not given his consent to co-authoring a book. 

"I can confirm that this morning, at the indication of the Pope emeritus, I asked Cardinal Robert Sarah to contact the publishers of the book requesting them to remove the name of Benedict XVI as co-author of the book itself, and also to remove his name from the introduction and conclusions," he said in a statement to Ansa news agency.

"The Pope emeritus in fact knew the Cardinal was preparing a book and had sent a short text of his on the priesthood" authorizing the cardinal to use it as he wished, he continued.

But the Pope emeritus "had not approved any project for a co-signed book, nor had he seen and authorized the cover. It was a misunderstanding, without questioning the good faith of Cardinal Sarah".

In comments to Catholic News Agency Deutsch, he insisted that Benedict had not written the introduction or conclusion of the book. 

"The name of Benedict XVI as 'co-author' of the book should be deleted and replaced with 'with a contribution by Benedict XVI,'" he said.

"His name must also be deleted after the introduction and the conclusions, because they are texts by Cardinal Sarah. It is simply a matter of correctly assigning the authorship. It is not about changes in content." 

The book appears today on the website of Ignatius Press with Benedict as co-author and also appearing on the front cover with the cardinal. 

Cardinal Sarah, however, said in a tweet that "considering the controversies that provoked the publication of the book From the depths of our hearts, it is decided that the author of the book will be for future publications: Card Sarah, with the contribution of Benedict XVI".

"However, the full text remains absolutely unchanged," he added. 

The book offers a defence of priestly celibacy, an issue that is being considered by Pope Francis in light of a meeting of the Synod of Bishops for the Pan-Amazonian region last October which expressed support for the ordination of married men as priests.

In his contribution to the book, Benedict writes that "it doesn't seem possible to realise both vocations [priesthood and marriage] simultaneously".

Pope Francis has previously expressed his own support for celibacy: "Personally I think that celibacy is a gift for the Church."

In a statement, Mark Brumley, President of Ignatius Press, said it had published the English version of the book "as we received it from the French publisher Fayard".

"The text we received indicates the two authors are Benedict XVI and Cardinal Sarah. That text also indicates that Benedict XVI co-authored an introduction and a conclusion with Cardinal Sarah, as well as his own chapter on the priesthood, wherein he describes how his exchanges with Cardinal Sarah gave him the strength to complete what would have gone unfinished," he said.

"Given that, according to Benedict XVI's correspondence and Cardinal Sarah's statement, the two men collaborated on this book for several months, that none of the essays have appeared elsewhere, and that a joint work as defined by the Chicago Manual of Style is 'a work prepared by two or more authors with the intention that their contribution be merged into inseparable or interdependent parts of a unitary whole,' Ignatius Press considers this a coauthored publication.

"Cardinal Sarah indicates the content of the book remains unchanged. That content, as noted, includes a coauthored introduction, a chapter by Benedict XVI, and a conclusion coauthored by Benedict XVI and Cardinal Sarah."