Geneva, Switzerland - The United Nations voiced alarm Wednesday at a recent spate of executions in the US, where two men are due to be put to death this week.

The UN rights office is "deeply concerned by the impending execution of two men" in Texas and Alabama on Thursday, spokesperson Seif Magango said in a statement.

"This would follow the execution of six people in five different US states over a 12-day period last month," he added.

"This rise in the rate of executions is deeply worrying."

Derrick Ryan Dearman is due to be executed on Thursday in Alabama, where he was reportedly convicted of murdering several people with an axe in 2016.

On the same day, Robert Roberson, an autistic 57-year-old, is scheduled to die by lethal injection at the state penitentiary in Huntsville, Texas, over the February 2002 death of his two-year-old daughter, Nikki.

Roberson's lawyers say the diagnosis of shaken baby syndrome, made at the hospital where his chronically ill daughter died, was erroneous and the cause of death was in fact pneumonia, aggravated when doctors prescribed a wrong medication.

Roberson's case has drawn the attention of the Innocence Project, which works to reverse wrongful convictions, best-selling US novelist John Grisham, Texas lawmakers and medical experts.

The death penalty "is incompatible with the fundamental right to life and raises the unacceptable risk of executing innocent people," Magango warned.

The UN spokesperson stressed that "evidence also suggests it has little to no effect in deterring crime."

There have been 19 executions in the US this year including the September 24 execution in Missouri of Marcellus Williams, whose case was also championed by the Innocence Project amid doubts about his guilt.

There were 24 executions across the US in 2023, according to the Death Penalty Information Center. The number peaked at 98 in 1999, and has mostly been on a decline since then.

The death penalty has been abolished in 23 of 50 states, while six others – Arizona, California, Ohio, Oregon, Pennsylvania, and Tennessee – have moratoriums in place.