A man was tortured and beheaded for sending WhatsApp messages when he was aged just 16, it is claimed.
Abdulkarim al-Hawaj, 21, was condemned as a 'terrorist' for communicating with others about an anti-government protest in the repressive Arab state.
He was allegedly chained, beaten and electrocuted before 'confessing' to his crimes, according to the human rights charity Reprieve.
Amnesty International called his trial a farce saying he was denied proper legal representation and forced to confess.
The organisation added that he had been told his family would be killed if he did not admit his guilt.
He was one of 37 men put to death in Saudi Arabia on Tuesday, bringing the total number of executions in the country this year to 105.
At least one of the men executed last week was crucified, according to reports.
The country's state news agency said the men had been convicted on terrorism charges, although Amnesty International claimed that 11 of them were convicted of spying for Iran.
Mr al-Hawaj, like the majority of the men executed last week, was a member of the Shi'ite minority in the Sunni-dominated country.
The Sun reported that the United Nations High Commissioner for Human Rights Michelle Bachelet said: "It is particularly abhorrent that at least three of those killed were minors at the time of their sentencing."
Mr Bachelet called on the Saudi regime to halt further capital punishment, including the executions of the death row trio Ali al-Nimr, Adawood al-Marhoon and Abdulla al-Zaher.
Iran's Foreign Minister Mohammad Javad Zarif slammed the United States for its silence over the latest executions.
He said: "After a wink at the dismembering of a journalist [Jamal Khashoggi], not a whisper from the Trump administration when Saudi Arabia beheads 37 men in one day."
