Hundreds of federal police headed to Rio de Janeiro on Sunday to battle a wave of gang violence ahead of a summit of South American leaders, next month's Carnival celebrations and the Pan American Games in July, the government said.

About 500 officers will be posted along the borders of Rio de Janeiro state to keep out weapons, drugs and criminals, the government's Agencia Brasil news agency reported.

Rio requested federal help after gang members attacked police stations and burned buses in late December. Some 19 people died in the street violence, including eight who were incinerated in a bus after criminals robbed passengers and set it ablaze.

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Over the next several months, the number of federal police patrolling around Rio could reach as many as 6,000, local media reported.

The first officers to arrive will fan out ahead of a two-day Mercosur trade bloc summit starting Thursday, when Brazilian President Luiz Inacio Lula da Silva will host the presidents of Argentina, Paraguay, Uruguay and Venezuela. Other South American leaders may also attend.

The police are members of Brazil's elite National Security Force -- 7,000 specially trained officers from all corners of Latin America's largest nation.

The force was created in 2004 after regular police had difficulty quelling extreme violence, and its officers have been deployed three times since. But they have never been sent to Rio or Sao Paulo, Brazil's biggest city, which suffered a similar wave of attacks in May that left nearly 200 people dead including some 40 police officers.

Rio residents on Sunday welcomed the arrival of the officers, but questioned whether they would be able to control gangs that dominate the street-corner drug trade.

"They have to come," said Manuel Dias, a 50-year-old travel agent. The criminals "have passed all limits. But no one knows if the troops will improve things."

Security is a major concern for the city as it heads into its busiest tourism season, capped by Carnival celebrations in February. Rio is also scheduled to host The Pan American Games, an Olympic-style competition for athletes of the Western Hemisphere, July 13-29.

Rio is one of the most violent cities in the world, with an annual homicide rate of 50 per 100,000 people. While the violence is usually confined to poor shantytowns, some of the crime in December spilled into well-heeled beach districts frequented by tourists.

Authorities say the gang blamed for the attacks was angered by the emergence of anti-crime militias in Rio's slums, reportedly made up of former and active duty police officers and soldiers.

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