In the operation, police also detained counterfeiters of euro bills, seizing about €200,000 worth.
State Police's Peteros Bauska said the operation was carried out quickly, thanks to a high level of cooperation between Latvian, US and European law enforcement agencies.
"It was thanks to colleagues in Europol and the US that enabled us to get such a quick result," Bauska said.
Raids were carried out on April 15, resulting in seven arrests. Four of those individuals remain behind bars.
The location of the printing press was in Riga but Bauska said it was "in a business space, not in a basement or some secret location."
US Secret Service representative Christopher Rohde said: "Over the last 16 months we have cooperated with Latvian State Police to investigate a large international counterfeit currency organization operating here in Riga.
"This investigation resulted in seven arrests and the seizure of proceeds from their counterfeiting activity. I want to commend out law enforcement partners in the Latvian State Police for aggressively investigating this case and supporting the prosecution of the defendants."
"We would rate this as a very sophisticated operation, a very serious operation that we have not encountered that often. This was a very sophisticated plant with very high capability of pumping out a lot of counterfeit."
The nationalities of the accused were not specified and officials were understandably reluctant to release too many details of an investigation they said was still ongoing as a widespread counterfeiting network was involved.
Police also revealed that last November a second, unrelated counterfeiting operation was shut down and three arrests were made. In that case, euro notes were being produced.