Saudi Arabia is set to imminently behead and crucify a protester who was arrested while he was still a minor, even as it takes up a position as chair of the UN Human Rights Council (UNHRC).

Ali al-Nimr is member of Saudi Arabia's Shia minority, and nephew of an outspoken Shia cleric Sheikh Nimr al-Nimr, who has also been sentenced to death for anti-government activities.

Ali was arrested in 2012 at the age of 17 in the predominantly Shia province of Qatif, during a protest inspired by so-called "Arab Spring" protest movements elsewhere in the Arab world.

He was convicted of numerous charges including belonging to a terrorist cell, incitement, stoking sectarianism and attacking police with molotov cocktails, Saudi state media reported.

His final appeal was rejected last week, the state-controlled Okaz website added.

The sentence is a particularly harsh one; not only will he be beheaded, but his body will be displayed on a crucifix in a practice mandated by Islamic law (Sharia) as a way of publicizing his fate and deterring others from following his example.

Human rights groups have appealed for the sentence to be commuted, and others have called for the gulf kingdom to pardon him as a gesture for the Muslim festival of Eid al-Adha, which began Wednesday.

Activists say he was tortured into issuing a confession, and note that according to the UN Convention on the Rights of the Child - to which Riyadh is a signatory - it is illegal to execute a child under the age of 18 at the time the crime was committed.

UN Watch head Hillel Neurer branded Saudi Arabia's appointment to the UNHRC "scandalous."

"It is scandalous that the UN chose a country that has beheaded more people this year than ISIS to be head of a key human rights panel," Neuer said. "Petro-dollars and politics have trumped human rights."

Incredibly, however, the US government has welcomed the appointment, with State Department Deputy Spokesman Mark C. Toner claiming to have no knowledge of al-Nimr's impending death sentence.

"I mean, frankly, it’s – we would welcome it. We’re close allies," he said in response to questions at a Tuesday press conference.

The Saudi government has yet to respond to the controversy.