Washington DC - The divided Supreme Court on Thursday blocked the creation of a publicly funded religious charter school, in a case that had tested the historic separation of church and state in the US.

Nearly all 50 states allow charter schools, of which there are some 8,000 in the country.

They are government-funded but operate independently of local school districts and are not allowed to charge tuition or have a religious affiliation.

The Catholic Church in Oklahoma had been vying to open the nation's first publicly funded religious charter school, Saint Isidore of Seville.

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But the court – deadlocked with four votes in favor and four against – upheld a ban imposed by a lower court in Oklahoma.

The Oklahoma Supreme Court ruled last year that the public funding mechanism for the proposed Catholic charter school in the central state was unconstitutional.

The separation between church and state is a bedrock principle in the US, rooted in the First Amendment of the Constitution. The separation has been upheld in many Supreme Court decisions.

During oral arguments in April, conservative justices had appeared open to allowing public funding of the school, a position backed by the administration of Republican President Donald Trump.

Conservatives hold a 6-3 majority on the nation's highest court, but Justice Amy Coney Barrett, another Trump appointee, has recused herself from the case, possibly because of previous connections to parties in the case.

That had left Chief Justice John Roberts, a conservative, as the potential swing vote.

The case was brought by the conservative Alliance Defending Freedom (ADF).