Congo Republic opposition leader Paulin Makaya was sentenced to two years in prison on Monday for his role in protests against a referendum proposing a third term for President Denis Sassou Nguesso.
Makaya was charged on four counts including "incitement to disturb public order" during a demonstration on October 20 when thousands of people took to the streets to protest the contitutional referendum.
Nguesso has ruled Congo for all but five years since 1979, and was re-elected in March after the referendum passed.
Makaya has denied the charges and his lawyer Eric Ibouanga said he plans to lodge an appeal to the ruling by the High Court of Brazzaville.
"The judgment brought by the correctional chamber is unjust and illegal," Ibouanga said.
Four people were killed at the march in October, when security forces opened fire after a crowd refused to disperse.
Residents said the violence in Brazzaville was the worst since Nguesso retook power in 1997 at the end of a brief civil war.
Makaya, 49, has already been detained for 8 months following his arrest. In addition to his sentence, he was charged a 2.5 million CFA franc ($4,183) fine.
Amnesty International had previously condemned his arrest on the grounds of freedom of expression and said that his pre-trial detention surpassed the four-month limit of Congolese law.