Yaound - A prominent lawyer's bid to end Cameroon President Paul Biya's 35 years in power has received a boost after nine opposition parties and grassroots groups backed his campaign, according to a statement seen by AFP on Tuesday.

Akere Muna, who hails from Cameroon's English-speaking minority, has vowed "zero tolerance for corruption, tribalism, nepotism and favouritism."

The nine organisations gave him their backing in a "platform for a new republic" that they agreed on Monday in the capital Yaounde, they said in a joint statement.

Muna is a former vice president of the anti-corruption campaign group Transparency International and former president of the Cameroon Bar Association.

He was "formally designated" as their only candidate for the presidency, the statement added.

Biya, in power since 1982, is one of Africa's most entrenched leaders.

The 84-year-old's rule has been characterised by ruthless exploitation, corruption and repression, according to critics.

He is yet to indicate if he will stand in elections, due before the end of 2018.

However, his political party, the Cameroonian People's Democratic Movement (RDPC), has presented him as the "natural candidate".

The election year comes as tensions remain high in Cameroon's two English-speaking regions, where pro-separatist demonstrations have led to violence and a crackdown.

Anglophones account for about a fifth of the West African nation's 23 million population. English-speaking protesters argue they are discriminated against by the French-speaking majority.

Demonstrators have demanded a federal state, while some secessionists have even called for independence.

Biya has firmly rejected any change to the status quo and imposed night-time curfews, restrictions on movement, raids and body searches.