PHOENIX (AP) — A federal appeals court panel on Tuesday issued an injunction blocking new Arizona abortion restrictions that are considered the most stringent in the nation, saying women likely would suffer irreparable harm if the rules are allowed to take effect.

The 9th U.S. Circuit Court of Appeals issued a stay blocking the Arizona rules last week while it considered an appeal from Planned Parenthood of Arizona and abortion rights groups. The court extended the stay into a full injunction on Tuesday.

Arizona Attorney General Tom Horne had asked the appeals court to lift the stay, saying Planned Parenthood did not have enough evidence to show the restrictions were detrimental. But the panel decided to block the rules at least through May 12, when it will hear arguments in the case.

Horne argued that Planned Parenthood Arizona hasn't proven that the Arizona regulations, which are based on a 2012 law, could cause irreparable harm. The organization is also unable to prove the regulations would place an undue burden on women's right to abortion, Horne said.

A lawyer for the Center for Reproductive Rights who is handling the case for Planned Parenthood and a Tucson abortion clinic said the court's three-page ruling bodes well for them.

"I think the fact they've said we have demonstrated a strong showing on the merits is a very good sign for us," David Brown said. "We've put on a very strong case that we're likely to win it — so we're very pleased."

The Center for Arizona Policy, an anti-abortion group that helped craft the law, said it believes the rules ultimately will be upheld.

"It's another temporary order. This one is far from over," CAP President Cathi Herrod said, noting that medical abortion restrictions in Ohio and Texas have been allowed to stand by federal courts and the Supreme Court allowed the Texas law to stand. "We remain confident that eventually the Arizona law will be enforceable just like the Texas and Ohio laws."

The abortion rules were released in January by the Arizona Department of Health Services. They ban women from taking the most common abortion-inducing drug — RU-486 — after the seventh week of pregnancy. Women had been allowed to take the abortion pill through nine weeks of pregnancy.

The rules also require that the drug be administered only at the Food and Drug Administration-approved dosage and that both doses be taken at a clinic. The dosage on the label, which was approved over a decade ago, is no longer routinely followed because doctors have found much lower dosages are just as effective when combined with a second drug, and women now usually take the second dose at home, avoiding what is often a long trip to a clinic.

Planned Parenthood Arizona estimates that 800 women would have had to get surgical abortions in 2012 if the rules had been in effect then. Proponents of the law say it protects women's health.

Separately, the Center for Reproductive Rights said Tuesday it has filed a lawsuit in Maricopa County Superior Court alleging that the new regulations violate the state constitution. They say the Legislature doesn't have the authorization to allow the Food and Drug Administration and the drugs companies to set state standards in Arizona. They also say the state Health Services Department violated its own public comment rules when it published the rules in January.