Mass protests against the tournament and deadly fan violence have put authorities on alert ahead of the start of the tournament on June 12.
The threat of hardline fans from across the border in Argentina or flying in from England and other European nations has accentuated the sense of urgency.
Prresident Dilma Rousseff this week ordered the army to reinforce police guarding the hotels and training camps for the 32 countries taking part, the defence ministry said.
Thirty infantry troops were sent Wednesday to Brazil’s base camp in Teresopolis, outside Rio de Janeiro. Brazil play the opening match against Croatia on June 12.
Some 1,800 private security guards have been assigned to each of the 12 World Cup stadiums. About 700 federal agents will also be drafted in if needed, officials said.
Organizers are also deploying banks of cameras, X-ray machines and metal detectors to keep potentially dangerous items out of stadiums.
They have already banned the “caixirola,” a trumpet-like instrument the government had promoted as Brazil’s answer to the vuvuzela, the horn that created a noisy stir at the 2010 World Cup in South Africa.
Some fans threw caixirola onto the pitch during test games last year. Authorities decided it was too risky and banned the trumpet as a potential weapon.
– Closed borders –
The security clampdown starts at Brazil’s borders. The government has held intelligence exchanges with Argentina, England and other countries over known hooligans.
“We have struck agreements through FIFA. The objective is to stop them (violent fans) from getting here and then, if they do, to keep them from entering the stadiums,” said President Dilma Rousseff.
Tens of thousands of Argentine fans are expected to cross the border to support their two-time champions.