Authorities are unsure what provoked the three-day encounter but say the Mashco-Piro may be upset by illegal logging in their territory as well as drug smugglers who pass through. Oil and gas exploration also affects the region.

The more than 100 members of Mashco-Piro clan appeared across the Las Piedras river from the remote community of Monte Salvado in the Tambopata region of Madre de Dios state from June 24-26, said Klaus Quicque, president of the regional FENAMAD indigenous federation.

They asked for bananas, rope and machetes from the local Yine people but were dissuaded from crossing the river by FENAMAD rangers posted at the settlement, said Quicque, who directed them to a banana patch on their side of the river.

The incident on the Las Piedras is chronicled in video shot by one of the rangers and obtained Monday by The Associated Press.

"You can see in the images there was a lot of threatening the intention of crossing. They practically reached mid-river," Quicque said by phone from Puerto Maldonado, the regional capital.