MEXICO CITY — The commando-style raid in the early hours of Monday unfolded with military might and coordination.

Dozens of gunmen blocked highways, burned trucks and cars, sealing off the perimeter of their target for hundreds of yards. The assailants, who were wearing flak jackets and driving in armored vehicles, used explosives and .50 caliber guns to blow the facade off a transportation company office in Ciudad del Este, a town in Paraguay near the smugglers’ haven in the border region with Brazil and Argentina. They killed a policeman, broke open the vault and then escaped — apparently fleeing by motorboats up the Paraná River — with millions of dollars.

The haul was initially estimated at $40 million, which would be roughly equivalent in today’s dollars to the amount lifted during the “Great Train Robbery,” the infamous 1963 theft of a post office train in England. Officials with the targeted company, Prosegur, which transports valuables, said the amount was less. Still, Paraguay news reports were calling the robbery the largest in the country’s history and the “heist of the century.”