After losing last-minute appeals, an Alabama death row inmate is hours away from undergoing the first nitrogen gas execution in the United States.

A lower appeals court and the United States Supreme Court have declined to vacate the cruel and unusual punishment described by Kenneth Eugene Smith's attorneys. For up to fifteen minutes, nitrogen is to be forced into his body through a mask.

Smith, aged 58, was found guilty in 1989 of an arranged homicide involving the murder of Elizabeth Sennett, the wife of a pastor. The execution of Alabama is slated to commence on Thursday.

Smith would be the first person in the United States and, according to the Death Penalty Information Centre, anywhere in the world to be executed by this method.

Wednesday night, attorneys for the inmate, who has been on death row since 1996, informed the sources that they were re-applying to the highest court of the country in an attempt to secure an eleventh-hour stay of execution.

Two years ago, Alabama attempted to execute the convicted murderer via lethal injection. Smith was one of two individuals found guilty on March 18, 1988, for the murder of Mrs. Sennett, 45 years old, in a hired assassination for $1,000 (£790).

A fireplace implement was used to beat her, and she was stabbed in the torso and neck; her demise was orchestrated to resemble a home invasion and burglary.

As a debt-ridden minister, her spouse had devised the strategy to amass insurance funds. Suicidal tendraction ensued as investigators approached.

In 2010, Smith's accomplice and fellow assassin John Forrest Parker was executed.

Smith acknowledged his presence during the murder of the victim, but stated he did not participate in the assault during his trial.

Smith's poisoning, according to the United Nations High Commissioner for Human Rights, could constitute torture or other cruel, inhuman, or degrading treatment; he has demanded an end to the practice.

Smith's attorneys filed a petition with the Supreme Court, contending that the practice of subjecting convicted individuals to repeated execution attempts infringes upon the Eighth Amendment of the United States Constitution, which safeguards against "cruel and unusual" punishment.

The appeal was not heard by the justices on Wednesday, and his request to suspend the execution was also denied. There were no public dissents from the justices regarding the ruling.

Smith had filed an additional legal challenge with the lower 11th US Circuit Court of Appeals, in which he questioned whether Alabama's nitrogen gas protocol was lawful.

On the contrary, the inmate's petition for an injunction was denied by the court in a ruling published on Wednesday evening.

Smith's solicitors stated that they would file a Supreme Court appeal once more.

His legal team contends that the "recently released and untested" nitrogen gas procedure exposes him to the danger of choking on his own vomit.

Alabama stated in a court filing that they anticipate his demise within minutes and loss of consciousness within seconds.

In the past, State Attorney General Steve Marshall characterised it as "possibly the most humane execution technique ever devised."

Due to the increasing scarcity of pharmaceuticals utilised in lethal injections, two additional states in the United States, including Alabama, have authorised the implementation of nitrogen hypoxia as an alternative execution method.