GENEVA (Reuters) - United Nations human rights experts called on Saudi Arabia on Monday to halt the imminent execution of six men sentenced to death for activities related to the 2011 Arab Spring.

They said that since the Saudis were all under age 18 at the time, imposing the death penalty on them would violate international law, including a treaty protecting children ratified by the kingdom.

Riyadh’s human rights record has been in the spotlight since the murder of Saudi journalist Jamal Khashoggi at its Istanbul consulate this month. There has also been growing international criticism of the Saudi-led coalition’s air strikes in Yemen that have caused heavy civilian casualties including children.

The charges against the six men are based on “criminalization of the exercise of fundamental rights, including freedom of assembly and expression”, the U.N. experts said in a joint statement which gave scant details.

“They were allegedly tortured and ill-treated, forced to confess, denied adequate legal assistance during trial and never had access to an effective complaint mechanism,” it added.

The men were tried in a Riyadh specialized court that handles terrorism-related issues and there is no known appeals process, a U.N. human rights official told Reuters.

A Saudi source, speaking on condition of anonymity, told Reuters that his understanding was that the men would not be executed, in line with recent changes to Saudi law.

However, the U.N. experts said that the revised law still allows for the death penalty to be imposed on defendants who committed crimes as juveniles between ages 15 and 18.

Death penalty sentences and executions for crimes committed by people under the age of 18 run contrary to international law and standards, they said. Saudi Arabia has ratified the U.N. Convention on the Rights of the Child, which forbids capital punishment in such cases.

“In these circumstances, the execution of these six individuals would constitute arbitrary executions,” the experts said.

The U.N. statement named the six as: Ali al-Nimr, Dawood al-Marhoon, Abdullah al-Zaher, Mujtaba al-Sweikat, Salman Qureish and Abdulkarim al-Hawaj.

The five independent experts, who include the U.N. investigator on arbitrary executions Agnes Callamard, said they were in contact with Saudi authorities regarding the cases.

Saudi Arabia is the world’s third biggest executioner, following China and Iran, Amnesty International said in its latest annual report issued in April.