(Reuters) - Rio de Janeiro police said on Saturday they had detained 19 people with a history of committing vandalism during protests as Brazil tries to pre-empt any potential violent demonstrations during Sunday's World Cup final.

Protests across Brazil have petered out since the month-long soccer tournament started on June 12, but authorities are taking no chances now that online videos are encouraging violent fringe groups to return to the streets when Germany plays Argentina.

Human rights advocates have condemned the detention of protesters, including lawyers and professors, in Rio and Sao Paulo. Police have used stun grenades and rubber bullets against demonstrators in both cities during the tournament, a popular event but also widely criticized by many in Brazil because of the $11 billion it cost the country to host it.

"The only goal is to neutralize, suppress and intimidate those men and women who have made ​​their presence on the street a form of expression in their fight for social justice," the Rio-based non-profit Justica Global group said in a statement on Saturday, adding more detentions were expected.

A police crackdown against students a year ago was seen as largely responsible for setting off a protest movement that brought more than a million people into the streets to air grievances over corruption and rising prices and to contrast the high cost of the tournament with the poor state of public services.

Since the World Cup began, Brazilians have been more interested in welcoming foreign visitors and watching soccer, but there is concern that protesting may be more appealing after Brazil's humiliating 7-1 loss to Germany. Some Brazilians are also unhappy that archrivals Argentina may win a trophy many expected would go to the home team.

About 26,000 security forces will work during the final match that will be attended by several presidents, while 1,500 private security guards will work inside Rio's Maracana stadium, according to the Justice Ministry.

Brazil has also blocked dozens of Argentine soccer hooligans with a history of stadium violence from attending the World Cup. Confrontations between fans of Brazil and Argentina have so far been limited to bar scuffles, but security has been stepped up on Argentina's game days.