Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Oklahoma plans to resume executions by using nitrogen or another gas to starve an inmate of oxygen because it cannot obtain the drugs needed for lethal injections, state officials said on Wednesday.

Corrections Director Joe Allbaugh said his agency is working to develop a protocol for the new method — which is certain to spark fierce legal challenges. No details of how it might work have been released.

"The victims of death row inmates have waited long enough for justice," Allbaugh said in a joint statement with Attorney General Mike Hunter.

"Trying to find alternative compounds or someone with prescribing authority willing to provide us with the drugs is becoming exceedingly difficult, and we will not attempt to obtain the drugs illegally."

Allbaugh also cited the difficulty of placing IVs in inmates, pointing to Alabama's recent failed attempt to kill Doyle Lee Hamm. "He was punctured 11 times," he said at a press conference. "I think that's inhumane."

Oklahoma is the latest state to explore alternative execution methods -- including the electric chair and firing squad -- because pharmaceutical companies will no longer sell their drugs to prisons for lethal injections.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The state hasn't carried out an execution in more than three years, and its last two lethal injections were bungled.

In 2014, Clayton Lockett regained consciousness during his execution because the IV wasn't properly placed. Although Lockett ultimately died, the mistake sparked outrage and prompted the White House to order a nationwide review of procedures.

The following year, Oklahoma successfully executed Charles Warner but used potassium acetate instead of potassium chloride as the third drug. "My body is on fire," Warner said after the injection began, according to witnesses.

Months later, the state had to cancel the execution of Richard Glossip because it had obtained the wrong drugs.

A bill signed in 2015 designated nitrogen hypoxia as the state's backup method if lethal injection is unavailable. Officials are now moving to make it the primary protocol.

"Using an inert gas will be effective, simple to administer, easy to obtain and requires no complex medical procedures," Hunter said.

Proponents say the gas induces unconsciousness and then depletes oxygen until there's brain death. The method has been used in assisted suicides but not in an execution chamber.

Some states have used the gas chamber in decades past, but that involved dropping pellets of poison like cyanide into acid, enveloping the inmate in vapor and causing a gruesome and sometimes protracted death.

Because executioners haven't tried hypoxia, death penalty opponents are sure to argue in court that there's no way to know how much an inmate will suffer, creating the risk of "cruel and unusual punishment" in violation of the Constitution.

Death penalty opponents are already expressing skepticism about the use of nitrogen and demanding that Oklahoma be transparent as it preps a new protocol.

"Who are the experts on nitrogen and nitrogen hypoxia who will be brought in? What research has the state undertaken to ensure the safety and legality of this new process?" said Dale Baich, who represents Oklahoma death-row prisoners.

"Without complete transparency, we have no assurance that executions won't continue to be problematic. The state should provide more answers before asking the people to trust it to carry out an execution in a humane and legal manner."

Sister Helen Prejean, the nun and anti-execution activist from "Dead Man Walking," blasted Oklahoma's plan as "human experimentation."