DAKAR, Senegal — Amnesty International says a military court in Cameroon has sentenced an opposition leader to 25 years in prison for hostility against the homeland and contempt of the president.

The international rights group said Monday’s sentence against Aboubakar Siddiki came after an unfair trial. It called for his release and that of well-known notary Abdoulaye Harissou who was sentenced to three years in prison for non-denunciation. The two, along with three journalists, have been held for more than three years and have attended 26 hearings in the Yaounde military court.

Amnesty welcomed the release of the journalists, but said the trials have been marred by irregularities, including witnesses refusing to testify because of intimidation and evidence collected under torture. It called the sentencing another effort by Cameroon’s authorities to silence opposition voices.