Sao Paulo, Oct 29 (IANS): A group of armed men set fire to three environmental agency offices in Brazil, after an operation carried out last week against illegal mining.

Hundreds of people, led by a group of garimpeiros (small-scale illegal miners), set afire the offices of the National Institute of Colonization and Agrarian Reform, the Brazilian Institute of Environment and Renewable Natural Resources and the Chico Mendes Institute for Biodiversity Conservation in the town of Humaita, located 800 km from Manaus, capital of the state of Amazonas, Efe news reported .

Ibama's superintendent in Amazonas, Jose Leland, told the Amazonia Real news portal that nearly 500 people took part in the attack in retaliation for an operation to combat illegal gold mining in the Madeira River.

"We've lost buildings, documents, archives, equipment and processes, but happily our workers are safe and sound," Leland said.

Members of the National Public Security Force are providing protection to some officials who live in Humaita in the wake of the attack, Leland said, adding that he will ask the Justice Ministry to beef up security while the police investigate the violent incident.

The garimpeiros carried out the attack on Friday night after an Ibama-led operation that destroyed 35 "balsas" -- boats that are used to carry the equipment the small-scale miners need to process the mined material and extract the gold.

"Despite this attack... we're going to continue with the operation and destroy the remaining balsas," Leland told Amazonia Real.

The garimpeiros are not licensed to carry out their mining activity and use no mechanisms to control mercury pollution, he said.