Brazilian military police in front of Congress hurled tear gas Tuesday at thousands of indigenous protesters, who responded by throwing spears and shooting arrows as a peaceful demonstration turned into chaos.
There were no reports of any injuries on either side.
Police said protesters got too close to a large fountain of water on the esplanade in front of Congress in Brasilia, Brazil's capital.
"The Indians did not comply with the agreement they made with police" about the boundaries of the protest, a police statement said. "They were threatening to invade Congress."
Demonstrators denied that, saying police were just looking for an excuse to remove them. They said that police had agreed the protesters could come close to the fountain and that the march was peaceful.
"Unfortunately, the brute force of the police caused this," said Kleber Karipuna, a protester who came to Brasilia from the northern state of Amapa. "It's natural that 3,000 Indians are going to respond" with spears and arrows.
Protesters said at least four people were arrested in the clash. Police did not provide details.
Brazil, Latin America's largest nation, is home to numerous tribes, many of which live in the Amazon region. Clashes with ranchers, logging companies and other businesses operating near or on their lands are common. However, indigenous leaders say the violence has gotten worse in the last year amid Brazil's economic crisis.
They have called for a campout in front of Congress all week to lodge a long list of complaints. They say the government of President Michel Temer is working to roll back protections in various parts of the Amazon and allowing ranchers and other big-money interests to steal their lands.