KANSAS CITY, Mo. — Casting it as “a question of exceptional importance,” Missouri has asked a federal appellate court to temporarily block and ultimately scuttle a ruling that requires the state to reveal one of its most-guarded secrets: who supplies its lethal injection drug.

Wednesday’s appeals urged the 8th U.S. Circuit Court of Appeals to suspend last week’s ruling by a panel of three of its judges, who unanimously rejected Missouri’s claim that disclosing how it gets pentobarbital could crimp its ability to obtain such chemicals for future executions.

Unless the 8th Circuit intervenes, Missouri must identify any sources by Sept. 16 to two Mississippi death row inmates who have subpoenaed the state for details about pentobarbital, which is a sedative. Missouri separately requested the full court to hear the matter.

The state insists “execution of its criminal sentences” is a “core state function,” and that the Missouri Department of Corrections “has demonstrated for years that if it reveals the identity of the supplier, then the supplier will no longer provide chemicals to Missouri.”

“This case presents a question of exceptional importance: Must the Missouri Department of Corrections disclose the identity of the supplier that provides the chemicals used in executions,” Wednesday’s appeal read. “The question is whether the subpoena places an undue burden on Missouri. It does.”

Missouri gets its execution drug from a compounding pharmacy and has shielded the source’s name, with similarly intense secrecy cloaking to what extent the drug is tested.

Arguing that Mississippi should consider adopting a one-drug execution method as Missouri, Texas and Georgia have done, inmates Richard Jordan and Ricky Chase have sued those states for specifics about their execution drugs as part of their federal challenge of Mississippi’s three-drug execution protocol, which they describe as torturous and unconstitutionally cruel. The inmates hope to show that alternatives to Mississippi’s execution protocol exist.

“It would be a classic Catch-22 to require our clients to produce evidence of a known, available alternative to Mississippi execution procedures but deny us the power to obtain the information we need to produce that evidence,” the inmates’ attorney, Jim Craig, said last week. He didn’t immediately reply to The Associated Press requests’ for comment regarding Missouri’s latest appeals.

Missouri has 25 death row inmates. Prison officials have argued any of the state’s execution drug providers “require the assurance of confidentiality,” given fears of threats and other harassment. One of the appeals alleged that, “as a matter of law, the identity of Missouri’s supplier is not relevant to Mississippi inmates.”

While acknowledging such disclosure “may have detrimental consequences for a state,” the 8th Circuit panel ruled last week that Missouri’s claims regarding a possible loss of drug supply were “inherently speculative” and “hearsay.”

Mississippi and other states have increasing struggled to obtain such drugs since 2010, as manufacturers refuse to sell them for executions. Mississippi says it intends to use another sedative, midazolam, which doesn’t render someone unconscious as quickly; the U.S. Supreme Court in 2015 upheld as constitutional Oklahoma’s use of midazolam.

Midazolam leaves an inmate at risk of severe pain during execution, Craig has argued.