The Bible is now one of the most objected to books at US schools and libraries, having been challenged on grounds of the sex and violence it contains, and for the legal issues it raises, it was announced this week.

The Bible featured for the first time on the American Library Association (ALA)'s annual list of the top 10 most challenged books, released on Monday, alongside Fifty Shades of Grey.

"You have people who feel that if a school library buys a copy of the Bible, it's a violation of Church and state," said James LaRue, director of the office for intellectual freedom at the ALA.

"And sometimes there's a retaliatory action, where a religious group has objected to a book and a parent might respond by objecting to the Bible."

Despite the high number of challenges, LaRue said the ALA does not object to having Bibles in public schools or libraries.

Having the Bible in a library "does not violate the separation of the Church and state as long as the library does not endorse or promote the views included in the Bible," he said.

The ALA defines a challenge as a "formal, written complaint filed with a library or school requesting that materials be removed because of content or appropriateness."

The Bible finished sixth on the list, which was topped by John Green's Looking for Alaska, with Fifty Shades of Grey coming second.

"Many of the books deal with issues of diversity," said La Rue. "And that often leads to challenges."

On the list were also two books telling stories of transgender people, Mark Haddon's The Curious Incident of the Dog in the Night-Time and Jeanette Winter's Nasreen's Secret School: A true Story from Afghanistan.

The list was compiled from 275 incidents of complaints, down from 311 in 2015.

The ALA did receive complaints about the Qur'an, but not as many as about the Bible, La Rue said.