The US Supreme Court accidentally leaked a major opinion on abortion rights, appearing ready to overturn part of Idaho's near-total ban.

According to a document published on the court's website then quickly removed, justices will rule that Idaho cannot deny emergency abortions to women whose health is in danger.

The court said the opinion, initially obtained by Bloomberg, was "inadvertently and briefly" published, and that its final decision had "not been released" but would be presented in due course.

Its publication however comes two years after the leaking of the court's decision to overturn the national right to abortion access, known as Roe v Wade.

Since then, a patchwork of abortion laws has been established as more conservative states, such as Idaho, restrict rights to the procedure.

The state is one of 14 banning abortion at all stages of pregnancy, with extremely limited exceptions.

It has defended its ban, saying that it allows abortions to save a patient's life and that it is not legally required to expand those exceptions.

The state's attorneys have said that the law, therefore, is not in conflict with federal law.

The court opinion on Idaho, which was published in full by Bloomberg, suggested that justices would rule 6-3 that it should not have become involved in the case so quickly.

Conservative justice Amy Coney Barrett, along with John Roberts and Brett Kavanaugh, wrote that the Supreme Court's intervention was premature as positions on the matter are "still evolving".

The report added that the court would reinstate an order that permitted Idaho hospitals to perform emergency abortions to protect patients' health.

If that is so, the case would continue at a federal appeals court.

According to the document posted by Bloomberg, one of the court's liberal justices, Ketanji Brown Jackson, noted in her opinion that she wanted a solid ruling, rather than a dismissal that moved the case back to another court.

"Today's decision is not a victory for pregnant patients in Idaho. It is delay," Justice Jackson wrote.

"While this court dawdles and the country waits, pregnant people experiencing emergency medical conditions remain in a precarious position, as their doctors are kept in the dark about what the law requires.

The accidental publication of the ruling, however, was swiftly met with cautious optimism from pro-abortion groups.

"With lives hanging in the balance, we hope this indicates a step forward for patients' access to emergency abortion care," the Pro-Choice Caucus of the US Congress posted online.

"Now, it is up to Scotus [the Supreme Court] to confirm that this is true and they will indeed protect that right and uphold federal law," the caucus added.

Alexis McGill Johnson, the president and chief executive of Planned Parenthood, said that "any decision that falls short of guaranteeing patients' access to abortion care in emergencies would be catastrophic".

The Biden administration sued Idaho over its near-total abortion ban in 2022, with Department of Health and Human Services Secretary Xavier Becerra saying that "women should not have to be near death to get care".

Idaho countered, saying that the federal law - known as Emergency Medical Treatment and Labour Act or Emtala - cannot supersede state law.

In a statement in April, the prominent anti-abortion group Susan B Anthony Pro-Life America called the Biden administration's lawsuit a "PR stunt" to spread "abortion lobby misinformation".

"The Emtala case is based on the false premise that pregnant women cannot receive emergency care under pro-life laws," said the organisation's public affairs director, Kelsey Pritchard.

“It is a clear fact that pregnant women can receive miscarriage care, ectopic pregnancy care and treatment in a medical emergency in all 50 states," she added.

The court's nine justices appeared divided during earlier arguments on the case in April.

In the document leaked on Wednesday, most of the court's conservative justices suggested that they were sympathetic to Idaho's case that doctors could not be compelled to break state law because of Emtala.

The three liberal justices - Sonya Sotomayor, Elena Kagan and Ms Jackson - on the other hand, all seemed doubtful that Idaho could, under Emtala, deny abortions to pregnant women facing serious health concerns.

In April, the Associated Press reported that at least six pregnant women had to be airlifted out of the state for emergencies since the law came into effect in January.

In 2023, by comparison, one patient required a similar emergency airlift.

In a separate ruling earlier in June, the Supreme Court unanimously rejected an effort to restrict access to the abortion pill mifepristone.

The decision, which came two years after the court rescinded the nationwide guarantee to an abortion, was welcomed by pro-choice activists.