DALLAS (AP) — Texas' prison system doesn't have to reveal where it gets its execution drugs, the state's top lawyer said Thursday, marking a reversal on an issue being challenged in several death penalty states.

Attorney General Greg Abbott, the Republican nominee for governor in the nation's busiest death penalty state, had rejected three similar attempts by the Texas Department of Criminal Justice to keep the drugs secret since 2010.

His decision is expected be appealed to the courts, meaning it likely won't take immediate effect

The department argues that the pharmacy providing the drug should remain secret in order to protect it from threats of violence. Lawyers for death row inmates say they need its name to verify the drugs' potency and protect inmates from cruel and unusual punishment.

Similar legal fights are ongoing in other death penalty states, including Oklahoma and Missouri, but courts — including the U.S. Supreme Court — have yet to halt an execution based on a state's refusal to reveal its drug supplier. The secrecy argument was used ahead of a botched execution last month in Oklahoma, though that inmate's faulty veins, not the execution drug, were cited as the likely cause.

Death penalty states have been scrambling to find new sources of drugs after several drugmakers, including many based in Europe, refused to sell drugs for use in lethal injections. That's led several states to compounding pharmacies, which are not as heavily regulated by the Food and Drug Administration as more conventional pharmacies.

Unlike some states, Texas law doesn't specifically say whether prison officials must disclose where they get their lethal injection drugs.

Abbot on Thursday cited a "threat assessment" signed by Texas Department of Public Safety director Steven McCraw as reasoning for his decision.

The assessment, a one-page letter dated March 7, said pharmacies "by design are easily accessible to the public and present a soft target to violent attacks." It adds that naming a pharmacy supplying execution drugs "presents a substantial threat of physical harm ... and should be avoided to the greatest extent possible."

Prison officials in Texas have previously provided little public evidence to support their claim that its execution drug supplier would be in danger if identified.

Also Thursday, Missouri's top lawyer said the state should establish its own laboratory to produce chemicals for use in executions rather than rely on an "uneasy cooperation" with medical professionals and pharmaceutical companies.

A state-operated execution drug lab would be a first.

Missouri is among several states that purchase execution drugs in secret from compounding pharmacies, the process shielded by state law. The Associated Press and four newspapers filed suit earlier this month in an effort to have the process made public.