The official poster of the FIFA WC Brazil 2014 is presented in Rio de Janeiro, Brazil, on January 30, 2013.
Brazilian President Dilma Rousseff said on Tuesday that her government accepted people's right to demonstrate during the World Cup but warned that it would not tolerate violence.
With less than 30 days to go to the tournament, military police deployed to the streets of Rio to protect a trickle of buses that were running in the face of a strike by bus drivers, although angry drivers still damaged 74 buses and there was travel chaos.
That came after a series of walkouts in Rio and other cities in other public sectors -- including the police -- and threats of general protests during the World Cup, which begins June 12, from people unhappy about the huge financial outlay for the tournament.
Last year's Confederations Cup was dogged by huge protests, some of them violent.
"Whoever wishes to demonstrate may do so, but not so as to hurt the Cup. Brazil is a democratic country... but democracy does not signify vandalism or damaging the country as a whole," Rousseff said in the northern city of Ceara.
The bus drivers' 48-hour strike followed another last Thursday in which 531 buses were trashed or set on fire, causing an estimated 17 million reais ($7.7 million, 5.6 million euros) in damage.
Businesses said last week's strike cost them 250 million reais, 60 percent of their daily turnover.
The bus drivers are demanding monthly salaries of 2,500 reais -- a 40-percent raise -- and an end to their double duty as drivers and fare collectors.
About two million of Rio's 6.3 million people depend on the city's privately run bus network, said municipal transport secretary Alexandre Sansao.
Hundreds of thousands of domestic and foreign tourists are set to flood Rio for the World Cup.
The city, which will host seven matches including the July 13 final, has been hit by a rash of strikes ahead of the tournament.
Teachers, bank security guards and the federal police have all gone on strike in recent weeks, the latter raising security fears by threatening to stay off the job during the World Cup.
In business hub Sao Paulo -- which will host six matches, including the kick-off -- police were meanwhile investigating after 11 vehicles parked outside a police station were torched.
Rousseff insisted that a 170,000-strong nationwide security force would guarantee public safety during the month-long World Cup.
She also dismissed criticism of Brazil's preparation for the event, with the hosts struggling to upgrade poor transport links and running behind schedule on several stadiums.
"The stadiums are coming on and the airports too. I think the Cup has all the ingredients for being a success," she said.