Opposition parties have called for the poll to be declared void, alleging fraud.

Tear gas was fired and demonstrators burnt tyres and barricaded roads on the streets of the capital Moroni.

Protests were also reported in other towns across the Indian Ocean archipelago.

An unspecified number of people were reportedly arrested during the protests.

A government spokesman accused the opposition of disturbing public order. The UN has appealed for restraint.

On Tuesday, the electoral commission announced that Mr Assoumani had garnered 63% of the vote in Sunday's ballot to secure a fourth term as president.

Only 16% of eligible voters took part.