(AFP) - The Maldives opposition on Monday began impeachment proceedings against the parliamentary speaker in an attempt to destabilise the president after allying with his powerful half-brother -- the former strongman leader Maumoon Abdul Gayoom.

The move came a day after the exiled opposition leader Mohamed Nasheed announced plans to take control of the 85-member Majlis, or parliament, in a unity pact with Gayoom.

The alliance marks an extraordinary turnaround for Gayoom. He is still nominally the leader of President Abdulla Yameen's ruling Progressive Party of Maldives (PPM) despite falling out with his half-brother.

On Sunday Gayoom appealed to members of the PPM to break ranks with the president and vote with the opposition on Monday to remove the speaker, Abdulla Maseeh Mohamed.

"In order to enable Majlis to fulfil its mandate in a democratic manner, I appeal to all MPs to vote NO to Maseeh tomorrow. Nation First!" Gayoom tweeted on Sunday night.

Gayoom retains influence over the party he once led, but it is unclear whether it will be strong enough to secure the impeachment, which would give the opposition more control over the legislative agenda.

Nasheed lives in exile in London after he was convicted on terrorism charges widely seen as politically motivated. He became the Maldives' first democratically elected president in 2008 but was narrowly defeated in 2013 elections by Yameen.

Last month he said he would return to the troubled Indian Ocean nation to run in 2018 presidential elections.

The Maldives constitution bars Nasheed from being a candidate because of the controversial 2015 criminal conviction.

But if his party can secure the support of enough lawmakers to win control of parliament, it might be able to overturn the law under which he was convicted, allowing him to return.

Yameen has presided over a major crackdown on political dissent in the nation of 340,000 that has raised fears over its stability and dented its image as an island tourism paradise.

Almost all key opposition leaders and a number of ruling party dissidents have either been jailed or fled into exile since Yameen took office in a controversial run-off election against Nasheed.

Gayoom, who ruled the country for three decades before he was ousted in 2008, has agreed to work with the opposition Maldivian Democratic Party to free those convicted of politically motivated charges.

"If we succeed, as we expect to, the president will be reduced to a lame duck and will have to carry out reforms and reverse the anti-democratic measures he has introduced," Nasheed told AFP during a visit to neighbouring Sri Lanka on Sunday.

He said the objective was to strengthen democratic institutions and ensure that 2018 elections are free and fair.

© Agence France-Presse