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 disclosure when he and lawyers for death row inmates asked a federal judge to suspend a lawsuit challenging 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.

Executions have been delayed in a handful of states because of drug issues, including Arkansas, where state officials on Friday asked the state Supreme Court to allow lethal injections to resume. A judge put executions on hold last week, after inmates challenged an Arkansas law that allows prison officials not to disclose where they get execution drugs. Oklahoma has a similar law.

The latest investigation in Oklahoma came after Gov. Mary Fallin called off the execution of Richard Glossip just hours before he was scheduled to die on Sept. 30. Prison officials discovered they had potassium acetate instead of potassium chloride, the specified final drug in Oklahoma's three-drug execution process.

A week later, a newly released autopsy report showed the state had used potassium acetate to execute Charles Warner in January.

Warner was originally 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, which was ultimately blamed on an improperly placed intravenous line, also prompted the state to delay executions as it investigated.

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

Dale Baich, an attorney for the inmates, said it would be difficult to pursue civil litigation amid an ongoing criminal investigation.

"So putting the case on hold while the investigations play out is a prudent thing to do," Baich said.

The autopsy report from 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. Experts on pharmaceuticals and chemistry told the AP that differences between the two forms could be relevant, because potassium chloride is more quickly absorbed by the body and more potassium acetate may be needed to achieve the same effect.

Questions about execution drugs also prompted delays in Mississippi, where a federal judge in August blocked the state from using pentobarbital or midazolam in lethal injections and ordered the state to seek his approval before trying any other drug. The state and inmates' attorneys say the ruling has stopped executions.

Executions have been on hold in Arizona since shortly after the nearly two-hour death of Joseph Rudolph Wood in July 2014. The state agreed to halt executions pending the outcome of a lawsuit filed by inmates seeking more information about execution protocols.

The Tennessee Supreme Court has put all executions on hold there while legal issues related to its lethal injection protocol are sorted out in court. Similar issues have blocked executions in Kentucky.