A Bulgarian special forces unit stormed the basement of a hotel in the Black Sea resort of Sunny Beach, the country's interior ministry said on Monday.

Officers from the unit, which targets organized crime, seized 100-euro and 500-euro notes, as well as 50 US dollar bills. The notes were found at the print shop and other hiding places. Some 30 sites were raided across the country.

The fake cash was said to be had a face value of €11.5 million and $2 million. Some notes were said to be stockpiled and ready for distribution.

Deputy chief prosecutor Ivan Geshev said that the printing operation was the "biggest illegal workshop dismantled in the past 11 years."

Prosecutors said the print shop had a sophisticated press that was making very high quality bills, with watermarks and security threads. The notes were to be handed over to Interpol for analysis.

The print facility had a sophisticated press that was making very high quality bills

According to the Bulgaria's Focus Information Agency, the counterfeiters were caught "red-handed" making fake money when the raid took place.

Four people were taken into custody during the operation, which took place on Saturday following a 10-month investigation by Europol and US intelligence.

Officers found facilities for making notes complete with watermarks and security threads

At the beginning of the 2000s, Bulgaria ranked among the biggest producers of fake US banknotes alongside Colombia, Chile and North Korea.

Read more: The never-ending story of Germany's ghost money

Bulgarian counterfeiters turned to copying euros after the country joined the European Union in 2007.

rc/aw (Reuters, AP)

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