Critics accuse President Paul Biya of ruling with an iron-fist

Leading rights group Amnesty International has condemned the decision of a military court in Cameroon to sentence an opposition leader to 25 years in prison for hostility against the homeland, trying to instigate a revolution and contempt of the president.

Aboubakar Siddiki - the leader of an opposition party in the north - was the "latest victim of the Cameroonian authorities’ strangling of opposition voices", Amnesty said in a statement.No credible evidence was presented to the court to convict him, it added.

He was arrested in 2014 after being accused of plotting to destabilise President Paul Biya's government.Mr Biya has been in power since 1982, and his critics accuse him of being authoritarian.

Several people have been killed and hundreds arrested in a crackdown on protests in English-speaking regions where people are complaining of marginalisation in mainly French-speaking Cameroon.

The military has also been battling fighters from militant Islamist group Boko Haram in the far north, who cross the border from Nigeria to carry out attacks.