Human rights experts are alarmed by Alabama’s plan to use an experimental method of execution to put a prisoner to death this month.

“We are concerned that nitrogen hypoxia would result in a painful and humiliating death,” experts said in a statement from the United Nations Wednesday.

The statement cites experts’ concerns over the “grave suffering” an execution by pure nitrogen inhalation may cause and notes a lack of scientific evidence to prove otherwise. Nitrogen hypoxia, though approved in three states, has never been used for the purpose in the U.S.

Alabama plans to use this method on Kenneth Eugene Smith on Jan. 25. Smith was convicted in a 1998 murder-for-hire plot and has served 34 years on death row. In 2022, Smith became the second Alabama death row prisoner in less than two months to survive an attempted execution by the state.

In addition to the use of untested drugs, U.N. experts called out the U.S’s history of botched executions and a lack of transparency in execution protocols Wednesday.

In 2022, a string of botched executions prompted Alabama Gov. Kay Ivey to put a moratorium on executions.

The Alabama Department of Corrections heavily redacted a document outlining protocols for carrying out executions by nitrogen hypoxia. According to what was made available, prisoners will be placed on a gurney, then fitted with a mask and breathing tube that pumps nitrogen gas for up to 15 minutes, slowly depriving the person of oxygen.

U.N. experts warned that experimental executions by gas asphyxiation violate several international agreements that prohibit torture and other cruel, inhuman or degrading punishment. “Punishments that cause severe pain or suffering, beyond harms inherent in lawful sanctions likely violate the Convention against Torture,” the statement noted. The Convention against Torture is an international treaty the U.S. signed in 1988, along with 83 countries.

Officials also named the Body of Principles for the Protection of All Persons under Any Form of Detention or Imprisonment, which guarantees that no detainee shall be subjected to medical or scientific experimentation that may be detrimental to his health.

In an appeal to authorities in Alabama as well as U.S. federal authorities, U.N. officials asked for a review of the state’s execution protocol.

Smith’s spiritual advisor, Rev. Jeff Hood, an outspoken opponent of the death penalty, filed a lawsuit last month over restrictions that prohibit him from being near Smith in the death chamber. ADOC forced Hood to sign a waiver acknowledging the deadly risks of exposure to nitrogen gas and asked him to remain 3 feet away from Smith during the execution. Hood found this protocol to be a violation of religious liberties.

U.N. experts added that they regret the continued use of capital punishment in the U.S. and that it contradicts global trends towards the abolition of the death penalty.

“Alabama’s plan to execute its people using nitrogen gas is terrifying and unconscionable,” Maha Jweidi, CEO of the Responsible Business Initiative for Justice (RBIJ), said. RBIJ collaborates with business leaders on criminal justice reforms, including death penalty abolition. Advocates at the organization have been following challenges to Smith’s execution closely as the execution date approaches.

“Instead of vengeance by any means necessary, Alabama should seek justice without perpetuating the cycle of violence our justice system is meant to break. The irreversible sanction of capital punishment has no place in a just society and does nothing to strengthen the rule of law.” Jweied said.