UNITED NATIONS, Feb. 19 (Xinhua) -- Two United Nations (UN) human rights experts have urged the U.S. government to halt the execution of a seriously ill person.

In a news release, Agnes Callamard, the UN Special Rapporteur on extrajudicial, summary or arbitrary executions, and Nils Melzer, the UN Special Rapporteur on torture and other treatments or punishments, also expressed concern that Doyle Lee Hamm, who is due to be executed in the U.S. state of Alabama on Feb. 22, may not have received a fair trial.

The execution, according to a UN report, is set to go ahead even though Hamm has cancer and medical professionals have previously had difficulty accessing his veins.

"We are seriously concerned that attempts to insert needles into Hamm' s veins to carry out the lethal injection would inflict pain and suffering that may amount to torture," said the UN rights experts.

The release also noted that judges have ordered a fresh medical report to be delivered by Feb. 20, two days before the scheduled execution.

"We urge the authorities to halt Hamm's execution, annul his death sentence, and hold a re-trial that complies with international standards, as we have received information indicating that his original trial did not fully respect the most stringent due process and fair trial guarantees," they added.

The Special Rapporteurs also said that imposing the death penalty in a manner that constitutes torture or cruel, inhuman or degrading treatment would render the execution arbitrary in nature and thus be in violation of the fundamental right to life.

UN special rapporteurs and independent experts are appointed by the Human Rights Council to examine and report back on a specific human rights theme or a country situation. The positions are honorary and the experts are not UN staff, nor are they paid for their work.

Hamm, 60 now, has been on Alabama's death row since 1987. He was convicted in 1987 of murdering a hotel clerk during a robbery and he reportedly confessed to the murder.

In recent years, Hamm has been diagnosed with lymphatic cancer and basal cell carcinoma. The Alabama Supreme Court has set an execution date for Feb. 22.