MALÉ - Former Maldives deputy leader Ahmed Adeeb has been jailed for 15 years for plotting to assassinate the president, the latest in a string of prosecutions of senior politicians and opposition figures in the troubled island nation.

Adeeb was convicted late Thursday of attempting to kill President Abdulla Yameen by setting off a bomb on his speedboat last September, his lawyer said.

Two of the vice president's military bodyguards were also convicted after the trial, which was held behind closed doors.

The verdicts mean almost all of Yameen's key rivals are in jail or exiled from the Maldives, a popular honeymoon destination that has been rocked by political turmoil in recent years.

They come weeks after Mohamed Nasheed, the country's first democratically elected president, was granted asylum in Britain.

Nasheed, whose legal team includes high-profile human rights lawyer Amal Clooney, was sentenced to 13 years in prison on controversial terrorism charges last year but was allowed to travel to Britain for surgery in January and was granted political asylum last month.

Adeeb, 34, was considered a close confidant of Yameen until he was dramatically impeached in November following allegations he was trying to topple the president.

Yameen escaped the blast unscathed, but his wife and two others were slightly injured. The FBI was called in to investigate the incident, but found no evidence the blast was caused by a bomb.

Reporters were barred from attending the trial after the court invoked national security concerns and said it would not make the hearings or verdict public.

Adeeb's lawyer, Moosa Siraj, told the Maldives Independent website he would appeal.

"The Criminal Court has barred me from calling the trial unfair, but we have concerns and intend to launch an appeal immediately," Siraj said.

Another lawyer who declined to be named said Adeeb's two bodyguards were also convicted Thursday, sentenced to 10 years each in jail.

The same court tried former prosecutor general Muhthaz Muhsin of conspiracy to kidnap the President by arranging a fake arrest warrant in February and sentenced him Thursday to 17 years in jail, his lawyer Husnu Al Suood said.

Adeeb, who enjoyed a meteoric rise until his impeachment, was given a separate 10-year sentence on Sunday on a terrorism charge relating to his role in cracking down on an anti-government protest in May 2015.

Opposition activists in the Indian ocean archipelago say dissidents risk arrest or exile under Yameen, the half brother of former strongman Maumoon Abdul Gayoom, who ruled the archipelago for 30 straight years until he was defeated in the first democratic election in 2008.

In July last year, Yameen sacked his then vice president Mohamed Jameel after accusing him of conspiring to seize power. Jameel is now living abroad in self-imposed exile.

Yameen's defence minister Mohamed Nazim was sentenced to 11 years in prison in March 2015 for trying to topple the government, and another ex-defence minister Tholhath Ibrahim was jailed for 10 years the following month.

And nearly four months ago, Yameen secured the jailing of Sheikh Imran Abdulla, leader of the opposition Islamist Adhaalath Party.

He was sentenced to 12 years after being tried for allegedly inciting unrest during an anti-government rally in 2015.