Ali al-Nimr
Activist Ali Mohammed al-Nimr remains in solitary confinement, awaiting execution in Saudi ArabiaFacebook

The mothers of five young Saudi prisoners sentenced to death by beheading made a passionate plea to the king to spare their sons' lives. The appeal followed reports that the Gulf kingdom is poised to execute more than 50 people convicted of terrorism.

In a public letter the women said the verdicts against the young dissidents, including Ali Mohammed al-Nimr, were based on confessions extracted under torture and the related trials fell short of international standards.

"The sentences handed down to our children are unique in the history of Saudi justice," the letter read. "As mothers of young men both deprived of their right to liberty and facing an unknown fate that may deprive them of their right to life, we demand that the Saudi government drop their sentences and order their retrial."

It concluded: "We stress that we will only stay silent over this crime if they kill us alongside our children." It was signed by Naima Ali al-Matrook, Fatima Hassan al-Ghzwe, Zahra Hassan al-Rebh, Amena Ahmed al-Saker and Nasra Abdullah al-Ahmed, mothers of five activists from the Shia minority arrested on sedition charges in 2012 when they were all teenagers.

Among them is al-Nimr, a 21-year-old dissident whose case has triggered uproar worldwide.The nephew of a vocal Shia cleric and activist, he was arrested aged only 17, for taking part in a protest.

He was forced to sign a confession under torture and has since been sentenced to death on a diverse set of charges, including attacking police, breaking allegiance to the king, setting up terror cells, rioting and robbing a pharmacy, according to human rights organisation Reprieve. Under Saudi Arabia's draconian legal system, he is to be beheaded and his body crucified in public.

The death sentence is expected to be carried out in the coming days as local media reported authorities were preparing for a mass execution of 55 convicts in a single day.

"These executions must not go ahead and Saudi Arabia must lift the veil of secrecy around its death penalty cases, as part of a fundamental overhaul of its criminal justice system," said James Lynch, deputy director of the Middle East and North Africa Programme at Amnesty International.

"Beheading or otherwise executing dozens of people in a single day would mark a dizzying descent to yet another outrageous low for Saudi Arabia, whose authorities have continued to show stone-faced cynicism and even open defiance when authorities and ordinary people around the world question their sordid record on the use of the death penalty".