The Brazilian armed forces have begun an operation in a vast area of the Amazon to tackle drug trafficking, logging and illegal mining.
More than 8,500 troops are taking part in Operation Agata 4.
They will be patrolling an area that stretches some 5,000km (3,100 miles) along Brazil's northern border.
The prospect of a big military operation caused some apprehension among Brazil's neighbours, including Venezuela.
But the Brazilian government says neighbouring countries were informed of the activities.
General Jose Carlos De Nardi, from Brazil's defence ministry, told BBC Brasil that he went in person to Venezuela, Guyana and Suriname to reassure them about the nature of the operation.
"I explained that it is aimed at combating crime and reinforcing the presence of the Brazilian government in the border region, one of the most remote areas of our territory," he said.
Air force jets and helicopters will provide support to the army, the navy and the federal police in their search for evidence of criminal activity in the Amazon.
The armed forces say they will bomb illegal landing strips, used by drug traffickers, and will seize airplanes used to bring cocaine and other drugs from the main drug-producing regions in Colombia and Bolivia.
They will also be looking for illegal logging and mining in protected indigenous land.
As part of the operation, a military boat will also be taking doctors and dentists to treat people in remote Amazon villages.
The region has been hit by one of the biggest floods in living memory.
There have been three such anti-crime operations over the past year.