Investigators said the euro, dollar and lev-printing scheme represents a severe attack on Bulgaria's and the European Union's financial systems.
Authorities in Bulgaria say they have seized a large quantity of counterfeit banknotes after dismantling an operation for their production in the northern town of Shumen.
Law enforcement agents on Tuesday said the fake bills, made in 50 Bulgarian lev, $50, and €500 denominations, had been released into circulation, passing through several banks and ATMs.
Boyan Raev, deputy head of the General Directorate for Combating Organised Crime, said the authorities found a significant batch of the Bulgarian 50-lev banknotes.
"The $50 bills were found in preparation, as well as the printing plates needed to produce these bills," Raev said at the press conference in Sofia. "€500 notes were also found ready and printed."
Two men with prior criminal records were placed under arrest, according to local authorities.
The group had successfully circulated some 37,500 Bulgarian lev in counterfeit banknotes and had produced around half a million euros in fake €500 bills.
According to an assessment by the European Central Bank, counterfeit euro banknotes were considered among the most elaborate fakes so far and have already been spotted in several EU member states.
"The analyses of the €500 banknotes found that this was a so-called superbill, namely a counterfeit of extremely high quality," authorities said.
According to Sofia, the operation was carried out in conjunction with US and European law enforcement agencies.
The investigators called it a very serious attack against the financial system of Bulgaria and the EU.