A Maldives court has convicted the country's former vice president of masterminding a plot to kill the president by exploding a bomb on his speedboat last year and sentenced him to 15 years in prison.

Ahmed Adeeb must serve a total of 25 years after the same criminal court sentenced him earlier this week to 10 years for possessing firearms.

Two of his military body guards were given 10 years each for being part of the plot.

Adeeb is the fourth high profile politician to be jailed on terrorism charges since Yameen Abdul Gayoom was elected president in 2013. The South Asian country is best known for its luxury island resorts.

Adeeb's lawyers said the court had barred them from speaking on the fairness of the trial even though they were allowed little time to prepare their defense. However they will appeal, lawyer Moosa Siraj said.

Adeeb still faces two more charges against him -- abuse of authority and corruption.

Gayoom escaped unhurt in the September blast while he was traveling by boat from the airport to the capital of this archipelago state. But his wife, an aide and bodyguard were wounded.

The government stood by its claim that the mysterious blast was an assassination attempt even though FBI investigators concluded they saw no evidence of a bomb blast.

Yameen appointed Adeeb, his once trusted protege, as vice president, last July after sacking his running mate in the 2013 election.

However, Adeeb became a suspect immediately after the blast and days later he was arrested and charged with plotting to kill the president. On Tuesday he was convicted in a separate case of possessing firearms, prohibited under Maldivian law.

Human rights groups have accused Gayoom of jailing opponents and potential challengers in order to tighten his grip on power.

Maldives former president Mohamed Nasheed, former defense minister Mohamed Nazim and Sheik Imran Abdulla, leader of a prominent opposition party, are the other leaders given lengthy prison terms since Gayoom assumed office. All the cases were criticized for a lack of due process.

Soon after Adeeb's conviction the judge also sentenced a former chief prosecutor to 17 years in prison for conspiring to have Gayoom arrested with a fake arrest warrant.

Muhthaz Muhsin had been detained since February along with a judge for allegedly issuing an arrest warrant against Gayoom for corruption.

Maldives has a long history of being ruled by autocratic leaders.

Gayoom's half-brother Maumoon Abdul Gayoom ruled the country from 1978 to 2008 until he lost to Nasheed in the country's first multiparty election.

Nasheed resigned in 2012 after weeks of public protests over his role in jailing a sitting judge. Last year he was convicted of ordering the military to kidnap the judge and sentenced to 13 years in prison. He was allowed to travel to Britain earlier this year apparently for back surgery and since he's been given asylum there.

Earlier this month, Nasheed, Gayoom's running mate Mohamed Jameel,  who also lives in Britain and supports Nazim, and Adeeb formed a united opposition in exile aiming to oust Gayoom from office.