ASUNCION, Paraguay -- Dozens of attackers armed with assault rifles used explosives to blast open the vault of an armoured car company early Monday and apparently escaped by boat into Brazil with a haul of cash, authorities said.

Officials said at least one police officer was killed and three civilians were injured in a blaze of gunfire and torched vehicles during the three-hour attack on the Prosegur company in the border city of Ciudad del Este.

Authorities did not release any information on how much money was stolen.

Up to 80 people may have been involved in the attack, said Arsenio Correa, investigations chief in the city.

"The criminals used snipers to guarantee the escape and torched more than 10 vehicles to distract the police," he said.

Video footage showed burned armored cars outside the crumbling remains of the company's building.

Ciudad del Este sits in the "Triple Border" region, where Paraguay, Brazil and Argentina meet and where contraband electronics, drugs and arms flow across porous borders.

Authorities said Brazilian gangsters were suspected of being behind the attack on the armed car company.

Regional police spokesman Anibal Lima said Brazilian police found AK-47 assault rifles inside two abandoned boats in the area's Itaipu lake.