The United States sued Idaho on Tuesday over a state law that it says imposes a "near-absolute ban" on abortion and also sought to block the Western state from prosecuting or disciplining doctors, according to a court filing.

The lawsuit, filed in US District Court for Idaho, seeks a preliminary and permanent injunction against the state prohibiting enforcement of the law and asked the court to rule that the state law violates federal statutes.

The lawsuit also alleges the state law interferes with the United States’ pre-existing agreements with hospitals under Medicare, referring to the federal health care programme for seniors.

"Today, the Justice Department's message is clear... if a patient comes into the emergency room with a medical emergency jeopardising the patient's life or health, the hospital must provide the treatment necessary to stabilise that patient," US Attorney General Merrick Garland said at a news conference in Washington announcing the filing.

"This includes abortion, when that is the necessary treatment," Garland added.

Tuesday's lawsuit marks the Justice Department's first legal battle over reproductive rights since the Supreme Court in June overturned the landmark 1973 Roe v. Wade ruling which recognised women's constitutional right to abortion.

Idaho in March became the first state to enact a six-week abortion ban modeled on a Texas law that empowers private citizens to sue abortion providers.

The law bans abortion before many women know they are pregnant and is modeled after Texas' six-week abortion ban. (Reuters)