ROME (AP) — A Vatican-affiliated Catholic charity made a last-minute appeal Tuesday to the U.S. state of Alabama to halt a planned execution using nitrogen gas, saying the method is “barbarous" and “uncivilized” and would bring “indelible shame” to the state.

The Rome-based Sant’Egidio Community has lobbied for decades to abolish the death penalty around the world. It has turned its attention to Thursday's scheduled execution of Kenneth Eugene Smith in what would be the first U.S. execution using nitrogen hypoxia.

Unless stopped by courts, Smith will be put to death for the 1988 murder-for-hire of a preacher’s wife. In legal filings, Alabama has said Smith will wear a gas mask and that breathable air will be replaced with nitrogen, depriving him of oxygen needed to stay alive.

“In many respects, Alabama seems to have the awful ambition of setting a new, downward standard of humanity in the already questionable and barbaric world of capital executions,” Mario Marazziti, in charge of Sant’Egidio’s death penalty abolition group, told a Rome press conference.

“We are asking that this execution be stopped, because the world cannot afford to regress to the stage of killing in a more barbaric way,” he said in one of several Sant'Egidio briefings taking place in Europe to draw attention to the case.

The Alabama attorney general’s office told federal appeals court judges last week that nitrogen hypoxia is “the most painless and humane method of execution known to man.”

But some doctors and critics say the effects and what exactly Smith, 58, will feel are unknown.

A petition from Sant’Egidio urging Alabama Gov. Kay Ivey to grant Smith clemency has been signed by 15,000 people, officials told reporters.

Marazziti noted that around the world, the trend has been to abolish the death penalty. According to Amnesty International, 112 countries have abolished it altogether, while others have issued a moratorium or don't practice it.

For those that still do, China, Iran, Saudi Arabia, Egypt and the United States had the most reported executions in 2022, Amnesty said.

Pope Francis in 2018 declared the death penalty inadmissable in all cases.

Alabama attempted to kill Smith by lethal injection in 2022, but the state called off the execution before the lethal drugs were administered because authorities were unable to connect the two required intravenous lines to Smith’s veins.