Guinea's opposition alliance Living Forces of Guinea (FVG) claims the vote, due to take place on September 21, is junta chief General Mamady Doumbouya's way of tightening his grip on power.

Military leaders have framed the referendum as a step towards the restoration of constitutional order in the west African nation.

Protests were outlawed in 2022 and the junta has set about arresting, pursuing and exiling opposition figures since it seized power in 2021.

On Friday, under heavy rainfall, AFP journalists saw police vehicles and officers stationed at roads, intersections, marketplaces and the outskirts of the capital.

The police presence was most marked in opposition strongholds in the suburbs of the coastal city.

Officers with assault rifles were deployed to areas described as strategic while an armoured vehicle equipped with a water cannon was parked on a normally busy thoroughfare.

By midday, there was little sign of protesters in some areas, where calls to take to the streets have been followed less due to fears of a crackdown.

The National Front for the Defence of the Constitution (FNDC), a member of the FVG coalition, said defence and security forces had been deployed to "prevent" the demonstration, in a statement published Friday.

The FNDC said warning shots to deter protests had been fired on Thursday night.

It added that five people had been "abducted", including "four pro-democracy activists" and one "kidnapped" FNDC member.

Guinean authorities have not responded to the allegations.

Doumbouya took office in September 2021 following a military coup that toppled Guinean president Alpha Condé, ending a rule of more than 10 years.

The proposed constitution does not explicitly state whether Doumbouya may run for president at the next election.

A "transition charter", created by the junta shortly after the military coup, states that no junta member, government official or institutional representative may run in the elections.

But that may change if the new constitution is adopted.

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