GENEVA, January 26. /TASS/. UN High Commissioner for Human Rights Volker Turk has expressed his regret over the execution of a US criminal with nitrogen gas as he questioned whether the method may be equal to torture or inhuman treatment.

"I deeply regret the execution of Kenneth Eugene Smith in Alabama despite serious concerns this novel and untested method of suffocation by nitrogen gas may amount to torture, or cruel, inhuman or degrading treatment," Turk said in a statement.

The death penalty was "inconsistent with the fundamental right to life," the UN official emphasized as he called on all member states to impose a moratorium on its use, "as a step toward universal abolition."

Smith, 58, was sentenced to capital punishment for participating in the murder-for-hire of a woman in 1988. He became the first person be executed by nitrogen suffocation, Attorney General of the State of Alabama, Steve Marshall, announced on January 25.