ASUNCION, Paraguay (AP) _ Gunmen in military-style uniforms stole $11.1 million as guards were about to load the money onto a plane headed for New York in the South American country's biggest robbery ever, authorities said Saturday.

Police said they had no immediate clues who was behind the robbery, which went off Friday evening without a shot being fired when heavily armed men overpowered security guards at Asuncion's international airport.

Norman Stark Coscia, an executive with the security service Prosegur that employed the guards, said the heist occurred on the tarmac as the money was being moved from one of its trucks to the cargo hold of the plane operated by Sao Paulo-based carrier Tam, or Transporte Aereo del Mercosur.

Authorities said the money had been collected from several private banks. The flight was scheduled to stop first in Buenos Aires, Argentina, then continue on to New York with the money destined for a bank in that city.

Local newspaper Ultima Hora said eight gunmen, their faces daubed in camouflage, pulled up to the plane in a pickup truck equipped with flashing lights like a security vehicle.

The newspaper added that the gunmen then overpowered the armored car's four guards, took the money in a matter of minutes and fled in the pickup truck down the tarmac.

Police did not confirm this account.