FARGO, N.D. — Gov. Jack Dalrymple of North Dakota approved the nation’s toughest abortion restrictions Tuesday, signing into law a measure that would ban most abortions and inviting a legal showdown over just how much states can limit access to the procedure.

The Republican signed into law three bills passed by the Republican-controlled Legislature. The most far-reaching law forbids abortion once a fetal heartbeat is “detectable,” which can be as early as six weeks into a pregnancy. Fetal heartbeats are detectable at that stage of pregnancy using a transvaginal ultrasound.

Most legal scholars have said the law would violate the Supreme Court’s finding in Roe v. Wade that abortions were permitted until the fetus was viable outside the womb, generally around 24 weeks.

‘’Although the likelihood of this measure surviving a court challenge remains in question, this bill is nevertheless a legitimate attempt by a state legislature to discover the boundaries of Roe v. Wade,” Dalrymple said in a statement.

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The Supreme Court, he added, “has never considered this precise restriction” in the heartbeat bill.

Abortion-rights advocates condemned his decision as effectively banning abortion in the state and framing the laws as unconstitutional and an attack on women. Without judicial intervention, the three bills are to take effect Aug. 1.

‘’They have no idea what kind of a sleeping giant they have awoken,” said Tammi Kromenaker, the head of the state’s only abortion provider, the Red River Women’s Clinic in Fargo. “I think that people are going to be much more aware of who we put in office and demand much more from our legislators.”

Dalrymple also affirmed measures to require doctors performing abortions to get admitting privileges at a local hospital, which could force the closure of the clinic, and to outlaw abortions for gender or genetic abnormalities. A similar law adopted by Mississippi last year is under challenge in federal court.

The signings come on top of a resolution already approved by the North Dakota Legislature last week to amend the state Constitution to assert that life begins at conception, a move that would give the fetus the rights of a person and outlaw virtually all abortions. The so-called personhood measure will go on the ballot next year.

Such measures have previously been voted down in Mississippi and Colorado.

Just three weeks ago, Arkansas lawmakers adopted what at the time was the country’s most stringent abortion limit, also tied to a fetal heartbeat and banning the procedure at 12 weeks of pregnancy. That is the point at which a heartbeat can be detected using an abdominal ultrasound.

The Arkansas and North Dakota laws have offered the first victories for an emerging faction of the anti-abortion movement that is frustrated by the limited progress in curbing abortions and hopes the Supreme Court might be ready for a radical rethinking. Similar measures to ban abortions when fetal heartbeats are detected are under consideration in several other states, including Kansas and Ohio.

The larger, established opponents of abortion including National Right to Life, Americans United for Life and the Roman Catholic Church have not supported heartbeat proposals, saying that until the court’s composition changes, they could be counterproductive.

These groups have instead pursued such measures as waiting periods, mandatory sonograms and stricter regulations on doctors and clinics, and in 10 states so far, bans on abortion at 20 weeks, an approach under challenge in the courts.