No executions will be scheduled in Oklahoma until at least next year, as the attorney general's office investigates why the state used the wrong drug during a lethal injection in January and nearly did so again last month, the office said Friday.

Attorney General Scott Pruitt made the announcement while he and several death row inmates' attorneys asked a federal judge to suspend a lawsuit that challenges Oklahoma's lethal injection protocol. The judge agreed after both sides said they wanted the case put on hold while Pruitt investigates how the state twice got the wrong drug.

The agreement came the same day that officials in Arkansas -- where a judge halted all scheduled executions last week -- asked the state Supreme Court to allow lethal injections to resume next week. Inmates there are challenging a state law that allows prison officials not to disclose where they get execution drugs. Oklahoma has a similar law.

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The latest investigation into Oklahoma executions came after Gov. Mary Fallin called off the execution of Richard Glossip just hours before his lethal injection was scheduled to begin on Sept. 30. Fallin stepped in when prison officials discovered they had potassium acetate instead of potassium chloride, the specified final drug in Oklahoma's three-drug lethal injection process.

A week later, a newly released autopsy report showed that Oklahoma used potassium acetate to execute Charles Warner in January, contradicting what the state publicly said it had used. Warner had originally been scheduled to die in April 2014, the same night as Clayton Lockett, who writhed and moaned before dying 43 minutes after his initial injection. Lockett's botched execution also prompted the state to put executions on hold amid an investigation.

The Oklahoma Court of Criminal Appeals has issued indefinite stays for Glossip and two other inmates who were set for execution this year.

Friday's court filing said Pruitt won't request any execution dates until at least 150 days after his investigation is complete, the results are made public, and his office receives notice that the prisons department can comply with the state's execution protocol.

"My office does not plan to ask the court to set an execution date until the conclusion of its investigation," Pruitt said in a statement.

An attorney for the inmates didn't immediately respond to a request for comment Friday.

The autopsy report prepared after Warner's execution on Jan. 15 said the Office of the Chief Medical Examiner received two syringes labeled "potassium chloride," but that the vials used to fill the syringes were labeled "single dose Potassium Acetate Injection." The execution log said the state used potassium chloride to stop Warner's heart, according to a copy obtained by The Associated Press.\

The next inmate scheduled to die was Glossip, but the governor stepped in after learning that a pharmacist -- whose identity is shielded by state law -- had given the prison potassium acetate. Prison authorities contacted the supplier, "whose professional opinion was that potassium acetate is medically interchangeable with potassium chloride at the same quantity," Oklahoma prisons director Robert Patton said at the time.

But experts on pharmaceuticals and chemistry told the AP that differences between the two forms could be relevant. They noted that potassium chloride is more quickly absorbed by the body and that more potassium acetate may be needed to achieve the same effect.

Questions about execution drugs also prompted the delay in Arkansas, where a judge has delayed all eight of the state's scheduled lethal injections through January. Death row inmates filed a lawsuit alleging the state's secrecy law violates a contract in an earlier settlement with prisoners that required information about execution drugs be released to inmates.

In Pennsylvania, Gov. Tom Wolf imposed a moratorium earlier this year. Calling the system of capital punishment error-prone and expensive, Wolf said the moratorium would remain in effect at least until he receives a report from a legislative commission that has been studying the topic for about four years.

In August, a federal judge temporarily blocked the state of Mississippi from using two drugs in executions, shutting down the death penalty in the state for now.

U.S. District Judge Henry T. Wingate issued a temporary restraining order saying Mississippi officials cannot use pentobarbital or midazolam, two drugs used to render prisoners unconscious.