A court in Angola on Monday sentenced famous rapper Luaty Beirão and 16 other activists to prison for plotting to overthrow President José Eduardo dos Santos during a book club meeting. Beirão, also known by his stage name Ikonoklasta, was handed a five-and-a-half year jail term for “rebellion against the president of the republic, criminal association and falsifying documents,” according to Agence France-Presse.

Beirão and 14 other young Angolan activists were arrested last year in late June after meeting to read and discuss Gene Sharp’s 1993 book on nonviolent resistance, “From Dictatorship to Democracy: A Conceptual Framework for Liberation.” Two others were accused for their links to the group but were not detained. Beirão, 34, went on hunger strike for five weeks last year to protest against his arrest. The activists have denied all charges against them.

The court in Angola’s capital of Luanda on Tuesday sentenced Domingos da Cruz, one of the activists who prosecutors identified as the “leader” of the group, to eight-and-a-half years in prison for planning a coup d’état and for criminal association. Michel Francisco, an attorney representing 10 of the accused, said he plans to appeal the sentencings, according to AFP news agency.

"Justice has not been done in a transparent way because things have been politicized and the judge only obeyed higher orders coming from the president of the republic," he told reporters Monday.

The court rulings have triggered outrage from global rights groups, saying the Angolan government has increasingly targeted activists in the oil-rich country. Human Rights Watch called the verdict “a ridiculous scandal,” while Amnesty International said the activists were sentenced by a “kangaroo court.”

“Today’s unjustifiable conviction and draconian sentences against these peaceful activists who should never have been detained at all demonstrate how Angolan  authorities use the criminal justice system to silence dissenting views. This ruling flies in the face of justice,” Deprose Muchena, Amnesty International’s director for Southern Africa, said in a press statement released Tuesday. “The activists have been wrongly convicted in a deeply politicized trial. They are the victims of a government determined to intimidate anyone who dares to question its repressive policies.”

Dos Santos, Africa’s second-longest serving leader, said earlier this month he would step down in 2018 after Angola’s next election in 2017. But the announcement has been met with skepticism because dos Santos, who has ruled since 1979, has made similar promises in the past. The 73-year-old president’s current mandate is slated to conclude at the end of next year.

In recent years, Angolan rappers like Beirão have used their music to help mobilize activists and lead a new youth movement to expose corruption and rights abuses by the dos Santos administration. Ahead of the August 2012 national elections, Beirão and other activists set up a system for voters to call in complaints of electoral fraud and compiled them on a website to push authorities to take action.

"We have led the way for other demonstrations in Luanda's poor suburbs and for war veterans who are seeking payment of overdue subsidies," Beirão told Reuters in an August 2012 interview. "The regime has been forced to react ... They see pressure will not come only from the opposition."