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 also may 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 said Tuesday that it got its sodium thiopental from Great Britain, the first time a state has acknowledged obtaining the drug from outside the United States 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.

The limited supply has also directly affected executions in California, Kentucky, Ohio 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 2012 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.

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