GENEVA: The UN human rights chief on Tuesday welcomed a pledge by US President Joe Biden to work towards abolishing the death penalty in the United States.

Biden, a Democrat, promised voters last year he would seek to end the federal death penalty, and took office last month as the country's first abolitionist president.

"I welcome the pledge by the new US Administration to work towards ending the death penalty, both at federal and state level," UN High Commissioner for Human Rights Michelle Bachelet said.

The punishment at a federal level was revived by Donald Trump last year after a 17-year hiatus caused in part by the increasing difficulty of obtaining drugs for lethal injections.

Merrick Garland, Biden's nominee for US attorney-general, on Monday told Congress his support for the death penalty had eroded amid concerns it disproportionately affected Black Americans and other communities of colour and that too many were wrongfully convicted.

"Deterrence is often an argument of those who oppose its abolition. However, there is no evidence that it deters crime more effectively than any other punishment," Bachelet said during a UN Human Rights Council debate.

"On the contrary, studies suggest that some states that have abolished the death penalty saw their murder rates unaltered or even decline," she said.

The US delegation, which has observer status, did not speak at the debate, held every two years.

The "vast majority" of countries have abolished the death penalty in law or do not carry out executions in practice, Bachelet said.