Guinea holds a long-awaited referendum on Sunday on a new constitution that could permit coup leader Mamady Doumbouya to run for president if he chooses to, something he vowed not to do when he seized power in 2021.

The military-led government in Guinea, which is home to the world's largest reserves of bauxite, has already missed a December 31, 2024, deadline it set for itself to return to civilian rule.

The presidential election is currently expected to take place in December.

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Critics fear the constitutional referendum is the latest attempt by a military-run government to legitimise its rule in West and Central Africa, where eight coups between 2020 and 2023 reshaped the regional political landscape.

While the referendum is seen as a step towards elections and the return to civilian rule in Guinea, Doumbouya's opponents have criticised it as a power grab by him.

Doumbouya has not said yet whether he intends to run for office. A transition charter adopted by his government after it took power said junta members would be barred from standing in the next election.

The referendum seems likely to pass because the two main opposition leaders, Cellou Dalein Diallo and deposed former President Alpha Conde, have called for a boycott of the vote.

Their parties are currently suspended, and Human Rights Watch has accused the government of disappearing political opponents and arbitrarily suspending media outlets.

The government has denied any role in disappearances but has vowed to investigate such allegations.

Voting centres were scheduled to open at 7 a.m. (GMT) on Sunday and close at 6 p.m. (GMT). It is unclear when the results are expected.

The new constitution would lengthen the presidential term from five years to seven, renewable once, and create a Senate, with one-third of senators directly appointed by the president.

In the final days of campaigning, the capital Conakry was dotted with small white posters featuring the word "Yes" next to a green checkmark.

On Thursday, S&P Global Ratings assigned Guinea its first-ever sovereign rating, B+ with a stable outlook. This makes Guinea the third-best-rated economy in West Africa, according to the ratings agency.

It noted, however, that despite some progress towards establishing a civilian administration, "social needs are high and tensions with the opposition are elevated with accusations of arbitrary arrests and rising pressure on the media".