Mozambique's main opposition leader, Venâncio Mondlane, has declared that he will install himself as president on 15 January after rejecting his defeat in presidential elections.

His announcement came as his supporters staged violent protests across the country to demand an end to the 49-year rule of the Frelimo party.

The capital Maputo was like a ghost town on Christmas Eve, with almost all businesses shut and people staying at home to avoid being caught up in the worst unrest in the city since Frelimo rose to power with independence in 1975.

Frelimo's offices, police stations, banks and factories have been looted, vandalised and set ablaze around the country.

Since Monday, at least 21 people have been killed in the unrest, the interior minister said late on Tuesday.

The latest unrest began on Monday after Mozambique's highest court upheld the victory of Frelimo's presidential candidate, Daniel Chapo, in elections held in October.

Mondlane had challenged the result, alleging that the poll was rigged.

In a Facebook live broadcast to his supporters on Tuesday, Mondlane said he rejected the ruling of the constitutional court, adding that he would assume the office of president on 15 January - the day that Chapo is due to be sworn in.

President Filipe Nyusi is due to step down at the end of his two terms.

It is unclear how Mondlane intends to take office, as he is currently in self-imposed exile in an unknown country.

He has frequently rallied his supporters via speeches on Facebook live, but has urged them to remain peaceful.

"We are with the people. We do not advocate any form of violence," Mondlane said in his latest address.

Chapo has not yet commented on his declaration.

October's election was the first time both of them had run for the presidency, with the electoral commission declaring Chapo the winner with 71% of the vote to Mondlane's 20%.

The constitutional court revised the result, giving the Frelimo candidate 65% and Mondlane 24%.

Rights groups say that more than 100 people have been killed in unrest since the elections.

They accuse the security forces of being responsible for many of the killings, but police commander Bernadino Rafael had previously told the BBC that his officers had been defending themselves after coming under attack.

Mondlane fled Mozambique after accusing police of threatening behaviour, and two of his aides were shot dead in October.

The 50-year-old evangelical pastor contested the election as an independent after breaking away from the main opposition Renamo party.

His support is strongest among young people, many of whom are unemployed and demanding change.

Frelimo fielded the 47-year-old Chapo as its youngest-ever presidential candidate.

He has previously rejected suggestions that he and Frelimo rigged the poll, saying: "We are an organised party that prepares its victories."