Drug barons have brought much of Rio de Janeiro to a standstill as Brazil's election campaign enters its final week.

Hundreds of shops were shut down across the city, including businesses around the fashionable Copacabana and Ipanema beaches.

This is unheard-of and completely absurd, especially in election week

Major Frederico Caldas police spokesman

Police were out on force as news spread that the drug lords had issued a threat, the motive of which is not yet clear.

Crime is a key issue for Sunday's elections in which veteran leftist Luiz Inacio Lula da Silva is strongly tipped to win the presidency for the first time.

Police said they were baffled by the shutdown - such orders have been issued by gangs in the past, but usually only to mark the death of a gang leader, and never before to the fashionable South Zone with its beaches.

But Rio's state governor, Benedita da Silva, suggested the threat was linked to the elections, in which she is standing for office again.

She pointed to a crackdown on crime in the city with 1,700 arrests made only recently.

Beached at the Copacabana

"This is unheard-of and completely absurd, especially in election week," police spokesman Major Frederico Caldas told Reuters news agency.

"All our battalions are in the streets to guarantee safety, all administrative work has been stopped."

The slums of Rio are notorious for violent crime

Police moved into the city's hillside favelas, or shantytowns, where the gangs are largely based, arresting at least nine people for delivering messages from the gangs.

Officers attempted to persuade shopkeepers to open up as businesses stood shuttered on Monday.

Guests at the Copacabana Hotel were being advised not to go into the streets and gunshots were heard in the morning in the Ipanema area.

One employee at a chemist's shop, Marcos Ribeiro, said the police were using the wrong tactics:

"That policing doesn't help because they stick around and then leave, but what comes next?"

Boost for Lula

Lula, as the left's presidential candidate is known, received a further boost on Monday as a new opinion poll increased his lead by two points.

According to the Vox Populi poll, Lula now stands at 43% with his nearest challenger, Jose Serra, at less than 18%.

Serra is hoping to keep Lula out of office a fourth time

Another poll, by Sensus, showed a slightly narrower gap with Lula on 40.6% and Mr Serra at less then 19%.

The prospect of a victory for Lula, who has fought and lost three previous presidential elections, has continued to upset Brazil's financial markets but the Workers' Party candidate said on Monday that the country needed to think beyond the markets' needs.

"Brazil won't go broke, Brazil won't go bankrupt," he told foreign reporters.

"We've already survived worse crises. What we need is for Brazilians to believe in themselves."

Mr Serra, the favoured candidate of outgoing President Fernando Henrique Cardoso, has remained upbeat, predicting he can get enough votes on Sunday to force Lula into a more challenging second round.