The Ministries of Defence and Justice, federal and highway police and the national force were sent to safeguard staff operating in the region and federal police have launched investigations into the attack.

In a joint statement over the weekend, the Brazilian Institute of the Environment and Renewable Natural Resources (Ibama) and the Chico Mendes Institute of Biodiversity Conservation (ICMBio) said despite the violence, they would continue their work to combat illegal gold mining in the Madeira River.

The Madeira River operation in the Amazonas and Roraima states is a joint project with the army, navy and national force.

In a translated statement, Ibama and ICMBio said the illegal mining financed land grabs and contributed to increasing violence in the field and required strong action by public institutions.

"The material damages will be assessed as soon as the region returns to normality, which should be guaranteed by the public security forces," they said.

Government agencies have been clamping down on illegal mining in the Amazon and are also investigating the alleged massacre of members of an uncontacted tribe by illegal miners.

In response to public pressure last month, Brazil repealed a decree that would have allowed mining and exploration in part of the Amazon known as the National Reserve of Copper and Associates (RENCA).