Police fired a smoke and noise bomb early Wednesday morning to disperse a group of Argentina fans celebrating a World Cup match victory late into the night.
Argentina beat Switzerland on Tuesday in São Paulo, and fans gathered late into the night on the streets of the Vila Madalena neighborhood in São Paulo, which has become an unofficial center of soccer festivities.
According to local media reports and images published by paper Folha de S.Paulo, hundreds of military police arrived around 2 a.m., and after a brief exchange, used what was termed as a "moral effect" grenade to break up the crowd of revelers, much to their confusion and dismay.
"Wasn't this supposed to be the World Cup party? Is this how you treat visitors?" asked one Argentina fan, according to the Folha report.
Police said they reacted to people throwing rocks, firecrackers and bottles.
For most of the first two and a half weeks of the FIFA World Cup, the tournament has gone relatively smoothly, with protests limited and visitors praising Brazilians as good hosts. But in a number of small incidents, Brazil's Military Police, widely criticized for years by human-rights groups, has been accused of using disproportionate force.
Journalists were injured by rubber bullets as they covered a protest on opening day in São Paulo, and human-rights groups criticized a police crackdown on a land occupation in Recife.
Argentina and Brazil are rivals in the World Cup, and both teams are among the eight still competing for the championship. The quarter-finals begin Friday.