A court in Gambia convicted 11 opposition supporters on Thursday on charges including unlawful assembly, rioting and conspiracy after they staged a protest in May calling for elections reforms in a case that has drawn international criticism.

The convictions of the United Democratic Party (UDP) supporters comes just a day after another group of 18 party members were jailed on similar charges.

Those convicted on Thursday participated in an April 14 march near the capital, Banjul, and refused to defend themselves before the court or participate in their trial.

"I therefore hold that the prosecution has proved the ingredients of the case beyond all reasonable doubts. I therefore hold all the accused persons guilty," Justice Simeone Ateh Abi announced in the court.

Each of the defendants was convicted on seven separate counts. The sentences for the individual charges ranged from monetary fines to three years in prison, with the combined sentences totalling 18 years imprisonment.

It was unclear, however, whether the accused would be allowed to serve those sentences concurrently.

Another group of 21 UDP supporters is still on trial.

The protests were a rare instance of open opposition to the iron-fisted rule of President Yahya Jammeh, who has ruled the tiny West African country for two decades after seizing power in a bloodless coup.

Rights groups accuse him of cracking down on political opponents figures as he eyes a December election, where he will seek his fifth term, after he scrapped term limits.

Both the United Nations and the United States condemned the arrests.