FLORENCE, Ariz. — Facing a nationwide shortage of a lethal injection drug, Arizona has taken an unusual step that other death penalty states may soon follow: get their supplies from another country.

Such a move, experts say, raises questions about the effectiveness of the drug. But it may also further complicate executions in the 35 states that allow them, as inmates challenge the use of drugs not approved by federal inspectors for use in the U.S.

Arizona officials said Tuesday that it got its sodium thiopental from Great Britain, the first time a state has acknowledged obtaining the drug from outside the U.S. since the shortage began slowing executions in the spring.

“This drug came from a reputable place,” Chief Deputy Attorney General Tim Nelson said. “There’s all sorts of wild speculation that it came from a third-world country, and that’s not accurate.”

Nelson said the state revealed the drug’s origins to let the public know that its supply is trustworthy and to dispel rumors. However, he did not name the company that manufactured it.

Without assurances of the drug’s quality, many questions will be raised, including its effectiveness and how it should be handled, and would serve as a basis for lawsuits, said Deborah Denno, a law professor at Fordham University.

“The impact could be huge,” Denno said. “The source of the thiopental is critical.”

A federal judge in Arizona blocked the Tuesday execution of convicted killer Jeffrey Landrigan because the state obtained the drug from a previously unidentified overseas source. The judge questioned whether it might be unsafe.

Landrigan’s lawyers contend he could be suffocated painfully if the sodium thiopental doesn’t render him unconscious. In lethal injections, sodium thiopental makes an inmate unconscious before a second drug paralyzes him and a third drug stops his heart.

Hospira Inc. of Lake Forest, Ill., the sole U.S. manufacturer of the drug, has blamed the shortage on unspecified problems with its raw-material suppliers and said new batches will not be available until January at the earliest.

There are no FDA-approved overseas manufacturers of the drug.

The limited supply has also directly affected executions in California, Kentucky and Oklahoma, and may affect executions in Missouri, which says its supply of sodium thiopental expires in January.

California officials say they acquired a dosage of 12 grams in September with a 2014 expiration date. But there was some dispute about the source. Hospira said its remaining supplies expire next year and California could only have obtained it elsewhere.

The state prison system would not address the discrepancy. “The state obtained the sodium thiopental lawfully from within the United States,” Terry Thornton, a corrections spokeswoman told The Associated Press.

Ohio, which spends about $350 for the drug for each execution, ran out of the amount prescribed by state procedures just three days before a May 13 execution. The state obtained enough in time but won’t say from where.

A few weeks ago, Kentucky’s governor held off signing death warrants setting execution dates for two inmates because the state is nearly out of sodium thiopental. The state’s lone dose expired Oct. 1.

Officials say they have tried unsuccessfully to get the drug from other states, and have gotten calls from states looking for it.