The left-wing candidate in Brazil's presidential election, Luiz Inacio Lula da Silva - known as Lula - has won a convincing victory in Sunday's run-off.

Thousands gathered in the streets to celebrate Lula's victory

Thousands of his supporters celebrated in the streets of Sao Paulo and Rio de Janeiro, with singing, dancing and fireworks.

Lula's government-backed opponent, Jose Serra, congratulated him in a telephone call and wished him well, one of Mr Serra's aides said.

In his victory speech, Lula invited the whole of Brazilian society - including business and trade union leaders - to join in building "a more just and brotherly nation".

He has repeated his undertaking that Brazil - suffering an economic crisis and burdened by debt - will abide by its obligations to the International Monetary Fund.

Almost all the votes have now been counted in the election, with Lula - whose birthday fell on election day - holding 61% of the vote to Mr Serra's 38%.

"So far, it has been easy," Lula told Brazilian national television.

"The hard part begins now. We will work around the clock to fulfil every one of our campaign promises."

The US Government has also offered its congratulations, with White House spokesman Ari Fleischer saying the US president "looked forward to working productively with Brazil".

Economic crisis

Lula's victory puts a left-wing government in power in Brazil for the first time in more than 40 years.

The BBC's Peter Greste, in Brazil, says that the strength of his support is a resounding endorsement of the former trade union leader's promises of economic prosperity fairly distributed to all Brazilians.

Lula has reached out to all sectors of the Brazilian political life

Many Brazilians are now hoping that Lula, seen as a champion of the poor, will do more to help those on the impoverished end of the social scale.

"This is our opportunity to consolidate our hopes for a Brazil which should be more just, and needs to care more about the needs of the people," supporter Marcos Xavier told the Associated Press news agency.

Lula has promised to adhere to the outgoing government's spending plans and its commitments to the International Monetary Fund.

However, he has warned that the international community "must know that we cannot have people suffering from hunger every day".

Move to centre

Lula, a former factory worker from an impoverished background, became a trade unionist and strike leader and a symbol of opposition to the military dictatorship in the 1970s and early 1980s.

He founded the Workers Party (PT) in 1980, but in recent years has moved to the political centre and dropped the anti-capitalist rhetoric that marked his three previous presidential bids.

He also sought to reach out to the financial community, which initially reacted negatively to his candidacy.

His choice of industrialist Jose Alencar of the centre-right Liberal Party as a running mate sent a strong message to the Brazilian business community, which has gradually warmed to him.