Pope Emeritus Benedict XVI wants his name removed as co-author of a new book on the issue of priestly celibacy, his personal secretary has said, claiming his name was erroneously attributed as co-author to a new book with a conservative cardinal.

Archbishop Georg Ganswein told Reuters that, at the former pope's behest, he had asked the principal author of the book, Cardinal Robert Sarah, to contact the publishers to make the necessary changes.

Publication of extracts from the book, "The Depth of our Hearts," by French newspaper Le Figaro on Sunday set off a storm within the Vatican, with some questioning why the 92-year-old Benedict would come out of retirement to co-author a book with ultra-conservative Cardinal Sarah.

Archbishop Gaenswein clarified that although Benedict had given Sarah passages he had written to use as the cardinal saw fit, "he hadn't approved any plans for a double signature book nor had he seen and authorised the cover".

"It was a misunderstanding, without questioning the good faith of Cardinal Sarah," he said.

In the book, which will hit bookshelves in France today, Benedict is quoted as saying he "cannot keep silent" about the divisive issue of whether or not to allow married men to become Catholic priests and coming down firmly against it.

Pope Francis is currently considering allowing it in remote locations, such as the Amazon, where communities seldom have mass due to a lack of priests. He is expected to publish his decision in the coming weeks.

Vatican experts had expressed astonishment that the retired pope would speak out in a public way on such a sensitive topic, and sources said Benedict had never authorised the book.

"Benedict XVI... never saw, nor authorised the cover, nor did he authorise the publication of a co-authored book," a Vatican source "very close" to the former pope told Elisabetta Pique, Vatican correspondent for Argentina's La Nacion.

Cardinal Sarah took to Twitter to defend himself, saying Benedict knew their collaboration would be a book, and that they had sent proofs back and forth for corrections.

He later issued a statement affirming his "affection" for Benedict and "obedience" to Pope Francis, and appeared to have been forced to row back on the issue.

"Considering the polemics caused ... it has been decided that the author of the book will be for future publications: Card Sarah, with the contribution of Benedict XVI," he said in a tweet.

"However, the complete text remains absolutely unchanged," he insisted.

The book features an essay by Benedict and another by Cardinal Sarah, with a co-authored introduction and conclusion. It has both the former pope and cardinal on the cover.

US publisher Ignatius Press said that their version of the book would remain co-authored as "the two men collaborated on this book for several months".