Four experts from the United Nations expressed their misgivings Wednesday with Alabama’s plan to execute a death row inmate with nitrogen gas, saying it would “result in a painful and humiliating death,” Ednews informs citing foreign press.

In a statement Wednesday, Morris Tidball-Binz, Alice Jill Edwards, Tlaeng Mofokeng and Margaret Satterthwaite, officials who work on health, executions, punishment and judicial issues, said the method may subject Kenneth Eugene Smith to “cruel, inhuman or degrading treatment or even torture.”

The experts said that Smith may be exposed to “grave” suffering and that there was no scientific evidence to demonstrate otherwise.

Smith, convicted of the 1988 murder-for-hire plot of Elizabeth Sennett, is currently awaiting a ruling on his appeal in the Middle District of Alabama for a preliminary injunction to stop his execution. He was convicted and sentenced to death by a vote of 11-1.

Nitrogen executions have never been used on a human being before. The American Veterinary Medical Association generally discourages its use in euthanizing animals. Other experts have expressed skepticism that the execution method will be humane.