Staying in the United States, and a death throw prisoner in Alabama is due to become the first person in the US to be executed using a nitrogen gas, a method which the United Nations has called cruel and inhuman. It will be the state's second attempt to execute Kenneth Eugene Smith, who was convicted in 1989 of murdering a preacher's wife in a hired killing. Despite growing calls for a stay of execution, the state authorities say they will press ahead with the death sentence. Correspondent Tom Bateman reports from at more in Southern Alabama.

Hidden in the Alabama woods, the jail meant to strike fear into every convict. For here, more than 160 inmates wait execution. But it is the fate of one, Kenneth Smith, sparking an outcry from campaigners and a legal battle going down to the wire. This prison was already among the top in the US for carrying out executions. But what is planned for Thursday. We'll put it in a new league, the first in history to gas an inmate to death using nitrogen. And that, warn experts, could cause convulsions, brain damage, but not death or other catastrophic mishaps. Smith has already been subjected to one failed execution by lethal injection. How are you, Esther? His supporters say trying again with an untested method breaks the law on cruel and unusual punishments. Thank you. This veteran campaigner against capital punishment remains in daily contact with Smith.

Hey, it's Kenny. Hey, sister. Good evening, hon. Hope you have been doing well. Me, so, so.

She sees his as a crucial test case against suffocation by the state.

She suffers from PTSD, from the terribly attempted botched execution. And now, one's going towards something which might even be worse.

It was two weeks ago today, 45-year-old Dorlene Elizabeth-Smith- Smith was convicted in 1989 of murdering the wife of an Alabama preacher who paid him and another man $1,000 each.

The jury recommended life in jail, but the judge overruled them and sentenced Smith to death. Sorry about that. Go ahead, Kenny. I Reached Smith on the phone, but he said he was too unwell to do an interview. He wrote later saying he was suffering panic attacks and felt he was being tortured. Alabama's governor, who can halt an execution, would didn't talk to us. Yeah, you can't. In a statement, the attorney general's office said it would proceed with the execution on Thursday. I don't know, man.

I like Alabama, and I tell you, it's good people.

And one local lawmaker who voted for the use of nitrogen gas rejects the UN's criticism.

I don't know about degrading. I don't know about inhumane. I think we're improving.

But this one's suffocation.

Yeah, I know. I don't remember exactly how the victim died, but I think it may be even better than don't know that, and I don't know that he did to the victim. I don't know that. I don't know that's a good way to die.

Is that what it's about for you, though? Is it? That sounds like retribution.

No, I don't think so.

Capital punishment in America has been in steady decline for years now. But on Alabama's death row, they fear this execution could create a lethal new turning point. Tom Bateman, BBC News at More, Alabama.