Arizona tried to illegally import a lethal injection drug that's not approved in the U.S. but never obtained it after federal agents stopped the shipment at the Phoenix airport, according to documents obtained by The Associated Press.

Arizona paid nearly $27,000 for sodium thiopental, an anesthetic also known as pentobarbital or Sodium Pentothal, that has been used to carry out executions but is no longer manufactured by FDA-approved companies, the documents said. When the drugs arrived via British Airways at the Phoenix International Airport, they were seized by federal officials and have not been released, according to the documents.

"The department is contesting FDA's legal authority to continue to withhold the state's execution chemicals," state Department of Corrections spokesman Andrew Wilder said Thursday.

Arizona and other death penalty states have been struggling to obtain legal execution drugs for several years after European companies refused to sell the drugs, including sodium thiopental, that are needed to carry out executions.

States have had to change drug combinations or, in some cases, put executions on hold temporarily as they look for other options. Utah has reinstated the firing squad and Tennessee reinstated the electric chair. Arizona used a mixture of midazolam, a sedative, and hydromorphone, a painkiller, in the botched 2014 execution of a convicted murderer Rudolph Wood, and has placed executions on hold since then.

The Arizona documents obtained by the AP were released as part of a lawsuit against the corrections department over transparency in executions. The AP is a party in the lawsuit.

They do not reveal what country or company Arizona tried to import the drugs from. Earlier this year, Nebraska was told by the FDA that it could not legally import the drug it needed to carry out lethal injection after the governor said the state had obtained sodium thiopental from India.

Other states also have looked into buying drugs from international pharmacies. Ohio, which has halted executions until at least 2017 because of a lack of drugs, sent a letter earlier this month to the FDA asserting that the state believes it can obtain a lethal-injection drug from overseas without violating any laws.

On Thursday, Texas said it had obtained a license from the U.S. Drug Enforcement Administration to import sodium thiopental. However, Texas Department of Criminal Justice spokesman Jason Clark could not say whether the state had purchased or received any drugs from overseas.

The Associated Press