Police confiscated 60 automatic rifles found in a cargo shipment Thursday at Rio de Janeiro's international airport, Brazilian authorities said.
The weapons were discovered in a container along with pool heaters in the cargo section of Galeao International Airport. Four people were arrested, and a Brazilian citizen is being investigated in Miami, where the shipment originated, officials said.
Police showed off the haul, which included AK-47s and AR-15s, at a news conference.
Rio State Security Secretary Roberto Sa said 250 automatic rifles in all have been confiscated the last five months in the state. Valued at over $1.2 million, he called the latest seizure as "the biggest in 10 years" in the state of Rio.
Authorities said they began investigating arms smuggling in 2015 after tracing the origin of a weapon used in the killing of a military police officer in the São Gonçalo neighborhood of Rio de Janeiro.
The probe unveiled a massive international scheme to buy military grade firearms, investigators said.
"This is a serious blow to these criminal organizations, to this international arms dealer," said Fabricio Oliveira, the head of the Brazilian Bureau of Firearms and Explosives. "Some details of the investigation are being kept confidential, as the investigations continue. This is only the beginning."
Police representatives said they planned to use the seized weapons, noting Rio state is struggling under budgetary constraints. Rio authorities declared a state of public calamity a year ago and have struggled to pay the salaries of the public sector ever since, including police.
The city of Rio de Janeiro, which hosted the 2016 Summer Olympics, has long struggled with violence. Heavily armed drug traffickers control many slums and shootouts are frequent.