The Saudi Arabian embassy in the UK has released a statement in which it rejects "any form of interference in its internal affairs" regarding the case of 21-year-old dissident Ali Mohammed al-Nimr, who has been sentenced to death by beheading for engaging in pro-democracy protests.

The London embassy tweeted, using the young activist's name as a hashtag:

The statement comes after David Cameron was challenged by Channel 4 News presenter Jon Snow on 6 October to explain why the British government agreed to a secret deal with the Saudis to allow both nations were elected to the UN Human Rights Council in 2013. The prime minister said he would personally raise the case of Nimr if there was an opportunity with the Saudi authorities. "We oppose the death penalty anywhere and everywhere in all our international contacts," he said.

Nimr, the nephew of a vocal Shia cleric and activist, was arrested in 2012, when he was 17, for taking part in a protest. According to human rights organisation Reprieve, 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.

Under Saudi Arabia's draconian legal system, he is to beheaded and his body crucified in public. The case has triggered uproar worldwide, with Amnesty International describing the trial as unfair and deeply flawed. Meanwhile, a Saudi court has upheld a beheading sentence against another young protester, Dawoud al-Marhoon.

Maya Foa, director of the death penalty team at Reprieve, said: "Ali al-Nimr's case has rightly prompted revulsion among the international community – it is therefore horrifying that the Saudi government is pushing ahead with plans to exact a similarly brutal sentence on another juvenile."