A federal judge on Friday struck down an Arkansas law that would ban most abortions starting at 12 weeks of pregnancy, one of the most restrictive such statutes enacted in the United States, declaring the measure unconstitutional.

U.S. District Judge Susan Webber Wright ruled that the law "impermissibly infringes a woman's Fourteenth Amendment right to elect to terminate a pregnancy before viability" of the fetus, as established by the U.S. Supreme Court.

Webber had previously barred enforcement of the measure while she reviewed a legal challenge to it brought by two Arkansas abortion providers.

As enacted, the Arkansas Human Heartbeat Protection Act would have banned most abortions at or after 12 weeks of pregnancy, if a fetal heartbeat could be detected by standard ultrasound.

Doctors who were found to violate the statute risked having their licenses revoked by the state medical board.

Exemptions were allowed in cases where the pregnancy resulted from rape or incest, if the life of the mother were in danger, or in cases of a gross fetal abnormality that made its survival impossible.

Webber's decision let stand the law's requirement that a woman seeking an abortion first undergo an ultrasound to determine whether a fetal heartbeat is present.

The American Civil Liberties Union, which represented the doctors in the lawsuit, applauded Wright's ruling.

"This ban would have inserted politicians into the deeply personal medical decisions of Arkansas women," said Rita Sklar, president of the organization's Arkansas chapter.

State Senator Jason Rapert, the primary sponsor of the measure, said he was "disturbed" by the ruling but added that the outcome "was not unexpected because of the posture of our courts for the last 40 years."

Rapert said he nonetheless was gratified that Wright had let stand "one of the strongest informed consent laws in the nation."

Governor Mike Beebe of Arkansas, a Democrat, vetoed the law after it was passed by the Republican-controlled state legislature in March 2013, citing its conflict with Supreme Court doctrine, but his veto was overridden.

The Arkansas attorney general, Dustin McDaniel, who had echoed Beebe's reservations about the bill, said he had not decided whether the state would appeal Wright's decision.

Rapert said he had urged McDaniel to defend the law, and said a national anti-abortion organization had volunteered to undertake the appeal "at no cost to the Arkansas taxpayers" if the attorney general would designate the group as "special counsel."

Alabama lawmakers earlier this month approved similar legislation. North Dakota passed a fetal heartbeat law last year that critics said could effectively ban abortions as early as six weeks after conception, but that measure was blocked by a federal judge in July.

About a dozen states, including Arkansas, have enacted prohibitions on abortions after 20 weeks of pregnancy, though some of those measures have also been enjoined by federal courts.