RIO DE JANEIRO — A motorcycle policeman can be seen on an Associated Press video firing what appeared to be a live pistol round at anti-World Cup protesters Sunday near Rio de Janeiro's Maracana soccer stadium.
During the small but violent and chaotic protest that played out about 1.5 kilometers (1 mile) from the stadium, another man in plainclothes who identified himself as a police officer also pulled a pistol and fired two shots into the air.
Pedro Dantas, a spokesman for the Rio de Janeiro security secretariat that oversees all security forces, said in a phone interview that if authorities verify the accuracy of the video, "we'll immediately open an investigation into the incident."
In a later emailed statement, the secretariat said riot police were hit by Molotov cocktails thrown by protesters. The statement didn't indicate if any officers were hurt.
The action took place around the beginning of the soccer game between Argentina and Bosnia-Herzegovina — the first World Cup match played in Maracana stadium since 1950.
"We're seeing tonight the same police brutality we've seen during the past year, and that's why we have to keep protesting," said Karen Rodrigues, a 23-year-old student at the demonstration that drew around 200 people.
Another protest occurred in the capital, Brasilia, but drew only a handful of participants, and a small protest also was held in Porto Alegre.
Mass protests broke out across Brazil during last year's Confederations Cup soccer tournament, the warm-up to FIFA's premier event. At that time, more than 1 million Brazilians took to the streets on a single day in the largest demonstrations this South American nation had seen in a generation.
But those mass protests died down after about two weeks. Since then, hundreds of smaller, violent protests have been seen across the country, though primarily in Rio de Janeiro and Sao Paulo.
The demonstrations have turned violent largely because of the almost constant presence of masked adherents to the "Black Bloc" tactic of protest. Black Bloc is a violent form of protest and vandalism that emerged in the 1980s in West Germany and helped shut down the 1999 World Trade Summit in Seattle.
The masked, young Brazilians are following the main anti-capitalist tenets of earlier versions, routinely smashing the windows of banks and multinational businesses, as happened Sunday night near Maracana.
The protest turned violent as demonstrators left the plaza where they gathered and marched toward the stadium on a main avenue. When they reached a security perimeter about a kilometer (half mile) from the stadium, riot police unleashed tear gas and stun grenades to disperse the crowd.
The protesters sprinted into a maze of smaller streets as World Cup fans drinking in small bars looked on. As the protesters regrouped and ran down roads, they frightened families with small children pressed themselves against buildings or took refuge in restaurants or taverns.
Before the violence broke out, the protesters marched through streets and chanted "FIFA, go back to Switzerland," referring to international soccer's governing organization. The protesters are angry over the lavish public spending on stadiums for the World Cup while conditions in Brazil's schools and hospitals remain woeful.