The mother of a 21-year-old Saudi currently facing death and crucifixion for taking part in anti-government protests in 2012 has pleaded for US President Barack Obama to intervene and prevent her son from being executed.

Nusra al-Ahmed, the mother of Ali Mohammed al-Nimr, says the punishment her son faces is both "savage" and "backwards" and repeated claims by other family members and organisations lobbying for her son's case that he was tortured during his interrogation.

Nimr's case has gained massive media attention since his appeal failed in September and the news broke that he could be beheaded and executed at any time. Labour leader Jeremy Corbyn raised the case in his inaugural party conference speech and David Cameron said the government would look into raising the issue with Saudi Arabia.

Much of the attention has focused on the crucifixion aspect of the sentence – which takes place after death under Saudi law – but equally the fact that when Nimr was arrested and originally sentence to death, he was 17. The sentence therefore violates the UN Convention on the Rights of the Child, to which Saudi Arabia is a signatory.

Speaking of the need for Obama to intervene, she told the Guardian: "He is the head of this world and he can, he can interfere and rescue my son... To rescue someone from harm, there is nothing greater than that. I mean my son and I are simple people and we don't carry any significance in this world but despite that, if he [Obama] carried out this act, I feel it would raise his esteem in the eyes of the world. He would be rescuing us from a great tragedy."

Saudi Arabia has rejected "any form of interference in its internal affairs" in a statement, while the Saudi ambassador to the UN, Abdallah al-Mouallimi, told the BBC the world should respect that the nation's internal affairs are its own business.

The anti-death penalty charity Reprieve, which highlighted Nimr's case in an opinion piece for IBTimes UK last month, issued a statement today that called America's silence on the case "woefully inadequate".

"Saudi Arabia's planned executions of Ali al-Nimr and another juvenile, Dawoud al-Marhoon, have rightly caused a global outcry. [...] The beheading of these two boys, who were arrested and tortured for merely attending protests, would be a grotesque miscarriage of justice. President Obama must listen to the call from Ali's desperate family, and step in now to urge the Saudis to change course," said Maya Foa, head of the death penalty team at Reprieve.