Texas prison officials are reviewing what they call the U.S. Food and Drug Administration's tentative decision to block it from importing a drug that could be used in executions.

The Texas Department of Criminal Justice had appealed the FDA's impounding last year of a sodium thiopental shipment, which the federal agency says has no legal uses in the U.S.

The FDA decision came in an April 15 letter to the department.

Sodium thiopental previously was part of a three-drug mixture used for executions in Texas, the nation's busiest capital punishment state. Since 2012, the state has been using a lethal dose of pentobarbital, another powerful sedative, as its execution drug.

Prison spokesman Jason Clark said Wednesday that the department is "exploring its options" regarding the lawful importation of execution drugs.