The United Nations and European Union condemned the United States on Friday after the country’s first execution of an inmate using nitrogen asphyxiation, an untested method that has reignited a debate about capital punishment, saying the method could amount to torture.

The southern state of Alabama put convicted murderer Kenneth Smith to death on Thursday by pumping nitrogen hypoxia into a facemask, causing him to suffocate. It was the first use of the execution method, rather than the usual lethal injection.

Alabama Attorney General Steve Marshall said “justice has been served” with Smith’s execution but UN human rights chief Volker Turk, the EU and US civil liberties groups expressed horror and concern.

“I deeply regret the execution of Kenneth Eugene Smith in Alabama despite serious concerns this novel and untested method of suffocation by nitrogen gas may amount to torture, or cruel, inhuman or degrading treatment,” Volker Turk, the U.N. High Commissioner for Human Rights, said.

“The death penalty is inconsistent with the fundamental right to life. I urge all states to put in place a moratorium on its use, as a step towards universal abolition.”

Ravina Shamdasani, spokeswoman for the UN human rights office in Geneva, said Smith was “clearly suffering” as he was put to death.

Rather than using such untried methods to conduct executions, “let’s just bring an end to the death penalty,” Shamdasani said. “This is an anachronism that doesn’t belong in the 21st century.”

A spokesperson for the 27-member EU, which opposes the death penalty, denounced the method of execution as “a particularly cruel and unusual punishment.”

Yasmin Cader of the American Civil Liberties Union said Smith “should have never been killed, let alone in such a gruesome manner.

“It’s past time for our country to put an end to the death penalty instead of inventing new and more heinous ways of carrying it out,” Cader said.

Smith, 58, was sentenced to death for the 1988 murder-for-hire of Elizabeth Sennett, a pastor’s wife.

After the nitrogen gas was administered, Smith “began writhing and thrashing for approximately two to four minutes, followed by around five minutes of heavy breathing,” local news outlet AL.com reported.

Smith appeared to be “holding his breath as long as he could” and there was “involuntary movement” and gasping, Alabama Department of Corrections Commissioner John Hamm told reporters.

Smith was pronounced dead at 8:25 pm (0225 GMT Friday).

Smith had survived one execution attempt. In November 2022, Alabama officials aborted his execution by lethal injection after struggling for hours to insert an intravenous line’s needle in his body.

--With inputs from agencies