Two French nationals have been sentenced to 10 and 20 years in prison for planning a coup against Madagascar's President Andry Rajoelina.

Paul Rafanoharana and Philippe François were prosecuted for endangering state security, criminal association and conspiracy to assassinate the president.

Twenty other co-accused were also given prison terms.

The French citizens' lawyer plans to appeal against the sentence.

"It is not what I expected, it is an unfair verdict... it is a political trial," defence lawyer Solo Radson is quoted as saying by AFP news agency.

The authorities say they uncovered the coup plot, dubbed "Apollo 21", after seizing emails, weapons and money during a raid in July.

It said details included plans to "eliminate and neutralise" a number of people, including the president.

François, a former colonel of the French army, was handed a 10-year sentence.

Rafanoharana, who is Franco-Malagasy and once served as an adviser to President Rajoelina, received 20 years. His wife was also given a five-year jail sentence.

Former Madagascar Prime Minister Victor Ramahatra was handed a five-year suspended prison sentence.

Madagascar has had a long history of coups and unrest since gaining independence from France in 1960.