The UN human rights chief on Monday condemned Saudi Arabia's execution of a record 81 people in a single day, and urged the kingdom to stop using the death penalty.
Michelle Bachelet said war crimes may have been committed if people were beheaded following court cases that do not offer proper fair trial guarantees.
Saudi Arabia said Saturday it had executed a record 81 people in one day for terrorism-related offences, exceeding the total number killed in the whole of 2021 and sparking criticism from rights activists.
All had been "found guilty of committing multiple heinous crimes", the official Saudi Press Agency reported, saying they included convicts linked to the Islamic State jihadist group, Al-Qaeda, Yemen's Huthi rebel forces or "other terrorist organisations".
"I condemn Saudi Arabia's mass execution on Saturday of 81 people on terrorism-related charges," Bachelet said in a statement.
The United Nations High Commissioner for Human Rights said that among those beheaded, 41 belonged to the Shiite minority, and had taken part in anti-government protests in 2011-2012. A further seven were Yemenis and one was a Syrian national.
"Our monitoring indicates that some of those executed were sentenced to death following trials that did not meet fair trial and due process guarantees, and for crimes that did not appear to meet the most serious crimes threshold, as required under international law," Bachelet said.
"I am also concerned that some of the executions appear to be linked to the ongoing armed conflict in Yemen.
"Implementation of death sentences following trials that do not offer the required fair trial guarantees is prohibited by international human rights and humanitarian law and may amount to a war crime."
The Saudi authorities should return the bodies of those executed to their families, the former Chilean president said.
"I am concerned that Saudi legislation contains an extremely broad definition of terrorism, including non-violent acts that supposedly 'endanger national unity' or 'undermine the state's reputation'," she added.
"This risks criminalising people exercising their rights to freedom of expression and peaceful assembly."
Bachelet said that Saudi Arabia was among 38 countries that continues to implement the death penalty.
The wealthy Gulf country has one of the world's highest execution rates, and has often carried out previous death sentences by beheading.
"I call on the Saudi authorities to halt all executions, immediately establish a moratorium on the use of the death penalty, and commute the death sentences against those on death row," Bachelet said.
"I also urge the Saudi authorities to bring the country's counter-terrorism laws fully into line with international standards."