It’s Brazil’s busiest border point – and with tens of thousands of people crossing back and forth each day from Paraguay and Argentina – security forces have stepped up checks amid fears of arms trafficking and possible militant attacks at the Rio Olympics.
The tri-border region around Foz do Iguaçu has long been seen as a smuggling hotspot.
“Police are investigating where the weapons come from,” said Fabiano Bordgnon, the head of Foz do Iguaçu federal police station.
“The majority are not produced in Brazil. They come from producing countries such as the United States, via Paraguay, and what do we need to do? We need to develop partnerships with these counties to prevent the entry of these weapons into Brazil.”
Last month, 12 people were arrested by Brazilian authorities on suspicion of supporting ISIL and discussing an attack during the Games.
It was the first time the government has admitted potential terrorist activity within its borders.
Police say they are monitoring a further 100 people with possible links to Islamic extremism, most of them in the tri-border area, or TBA as it is known in security circles.
The border region is home to a sizeable Muslim community.
Abdo Nasser Elkhatib, the imam of Foz do Iguaçu’s bright white mosque, stressed readiness to signal any extremism.
“If we come across anyone suspicious who could pose a security threat to the rest of the country, we are not going to ask what religion they belong to, what race or colour they are,” he said.
“We must take the necessary measures and report them to security officials.”
The border presents huge security challenges – especially in the days ahead.
But it is also a paradise for tourists and a place of breathtaking beauty, as home to the thundering Iguaçu Falls which were visited by the Olympic Flame last month.