Oklahoma's top education official has ordered schools in the state to begin incorporating the Bible into lessons, in the latest US cultural flashpoint over religion in the classroom.

A directive sent by Republican state Superintendent Ryan Walters said adherence to the rule was compulsory, requiring "immediate and strict compliance".

The rule will apply to lessons for all public school students aged from around 11-18.

It comes a week after Louisiana's governor signed a law directing all public schools in that state to display the Ten Commandments.

In a statement on Thursday, Mr Walters described the Bible as "an indispensable historical and cultural touchstone".

"Without basic knowledge of it, Oklahoma students are unable to properly contextualize the foundation of our nation, which is why Oklahoma educational standards provide for its instruction," he added.

Mr Walters, a former public school history teacher, was elected to his post in 2022 after campaigning on a platform of combating "woke ideology" and eliminating "radical leftists" from Oklahoma's education system.

His announcement, which covers grades five to 12, drew criticism from civil rights organisations and groups that advocate for a strict separation of church and state.

"Public schools are not Sunday schools," Rachel Laser, head of Americans United for Separation of Church and State, said in a statement quoted by AP news agency.

"This is textbook Christian Nationalism: Walters is abusing the power of his public office to impose his religious beliefs on everyone else's children. Not on our watch," she added.

Mr Walters has previously argued that secularists in the US have created a state religion out of atheism, by driving faith away from the public square.

In an op-ed last year for Fox News, he wrote that US President Joe Biden and the teacher unions had supplanted biblical values with "woke, anti-education values that tell students that they should treat their classmates differently depending on their race and sex and that they should be taught graphic sexual content at a young of an age as possible".

The Oklahoma superintendent's directive comes a week after Louisiana ordered every public school classroom in the state to display a poster of the Ten Commandments.

The Republican-backed measure was the first of its kind in the US, and governs all classrooms up to university level.

Days later, nine families in the state sued Louisiana, marking the start of what some expect will be a protracted legal battle.

The complaint, backed by civil rights groups, argues that such a display violates the First Amendment of the US Constitution, which guarantees freedom of religion, and that the display "pressures" students into adopting the state's favoured religion.

There have previously been legal battles over the display of the Ten Commandments in public buildings, including in courts, police stations and schools.

In 1980, in the case Stone v Graham, the Supreme Court struck down a Kentucky law requiring that the document be displayed in elementary and high schools. This precedent has been cited by groups contesting the Louisiana law.

In its ruling, the Supreme Court said the requirement "had no secular legislative purpose" and was "plainly religious in nature" - noting that the commandments made references to worshipping God.