By Agence France-Presse
United Nations, United States
He urged member states that still execute convicts to join the 170 countries that have halted or abolished the practice, warning that the risk of a miscarriage of justice is an "unacceptably high price" to pay.
"I want to make a plea to all states that continue this barbaric practice: please stop the executions," Guterres said at an event marking the 15th World Day Against the Death Penalty.
Capital punishment "does little to serve victims or deter crime," Guterres said, adding that most of the UN's 193 members do not carry out executions.
"Just last month, two African states - The Gambia and Madagascar - took major steps towards irreversible abolition of the death penalty," he said.
"In 2016, executions worldwide were down 37 per cent from 2015. Today just four countries are responsible for 87 per cent of all recorded executions," he added.
Those four countries are China, Iran, Saudi Arabia and Iraq, a UN official said, speaking on condition of anonymity.
Guterres also called for transparency from states where the death penalty is legal, asking them to let lawyers do their job.
"Some governments conceal executions and enforce an elaborate system of secrecy to hide who is on death row, and why," Guterres said.
"Others classify information on the death penalty as a state secret, making its release an act of treason."
This lack of transparency "shows a lack of respect for the human rights of those sentenced to death and to their families."