United Nations experts have called on Saudi Arabia to stop the pending executions of six people that were arrested and sentenced to death for actions taken while they were under the age of 18.

The group of experts said the six individuals were sentenced to death for alleged crimes that actually amount to the "criminalisation of the exercise of fundamental rights, including freedom of assembly and expression".

Since the individuals were minors at the time of the alleged offences, their death sentences run contrary to international law and would amount to "arbitrary executions," the experts said.

The experts, who include Agnes Callamard, the UN Special Rapporteur on arbitary executions, said the individuals were also subjected to torture and ill-treatment, were forced to confess, and didn't have access to adequate legal counsel.

The individuals were named as: Ali al-Nimr, Dawood al-Marhoon, Abdullah al-Zaher, Mujtaba al-Sweikat, Salman Qureish and Abdulkarim al-Hawaj.

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“As a State Party to the Convention on the Rights of the Child, Saudi Arabia is under an obligation to treat everyone under the age of 18 as a child," they said in a statement Monday.

"Children should never be subject to the death penalty, this practice violates an existing norm of customary international law and renders the punishment tantamount to torture."

Ali al-Nimr - who was arrested after participating in pro-democracy protests in the Gulf kingdom - is the nephew of Sheikh Nimr, a Saudi cleric who had called for reforms and was executed in January 2016.

Al-Nimr was sentenced to death by crucifixion at age 17, according to UK-based rights group Reprieve.

Heightened pressure on Riyadh

The call comes amid heightened pressure on Riyadh for its poor human rights record, and its role in the killing of Saudi journalist Jamal Khashoggi in particular.

A prominent columnist for the Washington Post, Khashoggi was killed inside the Saudi consulate in Istanbul on 2 October. While Saudi officials initially said the journalist left the building unharmed, they have since come out to say his murder was premeditated.

The Saudi-led war in Yemen has also been called into question since Khashoggi's death, with members of US Congress putting forward a motion to stop the US from funnelling weapons and other logistical support to the Saudi coalition.

Meanwhile, the UN experts said that while Saudi Arabia has amended legislation related to the punishment for juvenile offenders, the death penalty can still be handed out to children between the ages of 15 and 18.

“Saudi Arabia must ensure that children who have not benefited from a fair trial be immediately released and that those among them who were sentenced to death have their sentence commuted," they said.