Washington (AFP) - An Oklahoma man convicted of a double murder was put to death by lethal injection in the US state of Oklahoma on Thursday, the 24th and final execution to be carried out in the United States this year.

Phillip Hancock, 59, was executed at the Oklahoma State Penitentiary in McAlester, a spokeswoman for the state's Department of Corrections said.

He had been sentenced to death for the April 2001 murders of Robert Jett and James Lynch, members of a biker gang.

Though the Oklahoma Pardon and Parole Board had recommended that Hancock -- who claimed he had acted in self-defense -- be granted clemency, it was denied by Governor Kevin Stitt.

Hancock claimed he shot Jett and Lynch during a struggle after they tried to force him into a cage at Jett's Oklahoma City residence.

Shawn Nolan, one of Hancock's attorneys, denounced the governor for ignoring the clemency recommendation from the parole board.

"We are profoundly sad that Oklahoma executed Phil for protecting himself from a violent attack," Nolan said in a statement.

"This was a clear case of self-defense and the governor and the state ignored a wealth of evidence showing that Phil was fighting for his life," he said. "He fought to stay out of a cage to defend his life only to be caged and tragically killed by the state."

Even members of the governor's own Republican party condemned the execution, including State Representative Kevin McDugle, who called it "simply not justice."

McDugle said in a statement that he had learned of "serious problems in Oklahoma's death penalty system" while following the case.

He called for a halt to any further executions in the state "until we can ensure that only people who truly deserve capital punishment are sentenced to death."

US support for death penalty down

No further executions are scheduled in the United States for the remainder of the year.

According to the Death Penalty Information Center, 2023 was the ninth consecutive year with fewer than 30 people executed in the United States.

The 24 people executed in 2023 -- 23 men and one woman -- were six more than the 18 executed in 2022, the DPIC said in its annual report.

"Most of the prisoners who were executed in 2023 would likely not have been sentenced to death if tried today due to significant changes in the law, prosecutorial decision-making, and public attitudes over the past few decades," the DPIC said.

"Today, they would have powerful arguments for life sentences and decisions from juries who better understand the effects of mental illness, developmental impairments, and severe trauma."

According to a recent Gallup Poll, 53 percent of Americans support the death penalty for someone convicted of murder, the lowest level since 1972.

Capital punishment has been abolished in 23 US states, while the governors of six others -- Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee -- have put a hold on its use.

Executions were carried out in five states this year: Alabama, Florida, Missouri, Oklahoma and Texas.

The death penalty has been primarily carried out by lethal injection in recent years, but Alabama intends to execute an inmate next year using nitrogen gas.

Alabama Governor Kay Ivey has set January 25 as the execution date for Kenneth Smith, 58, who was sentenced to death for a 1988 murder.