Comoros President Azali Assoumani pledged on Sunday to work for peace and rapidly grow the economy as he was sworn in for his fourth term in office, following a tense January election which his opponents claim was tainted by voter fraud.

One person was killed and at least 25 injured in violent protests that erupted in the country, a group of three islands off the coast of Mozambique, after the election body declared him re-elected to another five-year term with 63% of the vote.

Comoros, with a population of about 800 000, has experienced around 20 coups or attempted coups since winning independence from France in 1975 and is a major source of irregular migration to the nearby French island of Mayotte.

Opposition leaders claimed the latest presidential poll was rigged, alleging instances of ballot stuffing and of voting being ended before the official closing time. The government denied the claims.

"Disputes after the elections are not a Commorian exception. I thank the Commorians for the renewed trust, I will not disappoint you," Assoumani, wearing a green and yellow sash, said at a ceremony in a stadium in the capital Moroni.

"After this inauguration, I invite civil society, the opposition and all political actors to put aside differences in favour of peace and democracy," said the former army officer, adding he would grow the economy at 5% per year.

Assoumani first came to power through a coup in 1999. He stepped down in 2002 and then won elections 14 years later. Constitutional reforms in 2018 removed a requirement that the presidency rotate among its three main islands every five years, allowing Assoumani to seek re-election in 2019.