Brazil began deploying some 30,000 troops Saturday to secure its borders as it prepares to host the World Cup that kicks off next month.
The operation involving the army, navy and air force will extend over the 16,900-kilometer (10,500-mile) frontier separating the South American giant from its 10 neighbors.
The internationally coordinated effort is part of a strategic border security plan announced by President Dilma Rousseff in June 2011.
"It is the single largest mobilization carried out by the state to combat illegal activity from the north to the south of the country," the government said in a statement.
A similar security operation took place ahead of last year's Confederations Cup, widely regarded as a test run for the World Cup extravaganza that will see football matches held in 12 cities.
That two-week operation netted nearly 19 tonnes of drugs, along with weapons and explosives.
The latest operation will target crimes including drug and arms trafficking, as well as illegal immigration. It will also provide medical care for needy communities.
It will span 710 cities and cover a distance of 110 kilometers from the borders, where security will be stepped up at crossings. Rivers and lakes will also be patrolled.
Globo television showed images of authorities inspecting vehicles, including trucks and passenger buses.
Along Brazil's border with Argentina, the troop deployment began at midnight, with checkpoints set up near the Uruguaiana International Bridge that links the two countries over the Uruguay River.
The Defense Ministry has not specified how long the operation will last for strategic reasons, with a spokesman telling AFP the military didn't want to "give advance warning to criminals."
Officials declined to confirm reports that a similar security operation could be carried out during the actual FIFA tournament, which runs from June 12 to July 13.
Brazil expects to welcome more than 600,000 foreign tourists for the massive sporting event, and is anticipating the internal displacement of more than three million locals.
Brazil shares borders with Argentina, Bolivia, Colombia, French Guiana, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela.
More than half of the border zones pass through rivers, lakes and other waterways.