Louisiana has become the first US state to order that every public school classroom up to the university level must display a poster of the Ten Commandments.

The Republican-backed measure signed into law by Governor Jeff Landry on Wednesday describes the commandments as "the foundational documents of our state and national government".

The law is expected to be challenged by civil rights groups, which argue that it contravenes the separation between church and state enshrined in the first amendment to the US Constitution, the so-called Establishment Clause.

It says: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."

The state law requires that a poster include the sacred text in "large, easily readable font" on a poster that is 11 inches by 14 inches (28cm by 35.5cm) and that the commandments are "the central focus" of the display.

It will also be shown alongside a four-paragraph "context statement" which will describe how the commandments "were a prominent part of American public education for almost three centuries".

The posters must be on display in all classrooms receiving state funding by 2025 - but no state funding is being offered to pay for the posters themselves.

Similar laws have recently been proposed by other Republican-led states, including Texas, Oklahoma and Utah.

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

In 1980, the US Supreme Court struck down a similar Kentucky law requiring that the document be displayed in elementary and high schools.

In a 5-4 vote, the high court ruled that the requirement that the Ten Commandments be posted "had no secular legislative purpose" and was "plainly religious in nature".

The court noted that in addition to criminal matters like killing and stealing, the Ten Commandments also made references to worshipping God including observing the Sabbath day.