After a nearly year-long investigation, Moldovan police also seized 200 grams (7 ounces) of uranium-238, one kilogramme (2.2 pounds) of mercury and 1 kg of "an unidentified radioactive material," Interpol said in a statement.
"The uranium, smuggled into the country by train, has a value of 1.6 million euros (USD 2 million)," the statement said.
"The radioactive substance can be used in the production of dirty bombs, which could cause massive destruction in the hands of a terrorist group."
The arrested suspects, aged between 32 and 75, belonged to a criminal ring and had knowledge of radioactive substances, the global police organisation said.
While radioactive uranium-238 is not suitable for a nuclear weapon, it can be used to make a dirty bomb, a conventional explosive that contains radioactive material.
Moldovan police said earlier this week they believed uranium-238 had been brought to Moldova from Russia on a regular passenger train.
Authorities nabbed the gang after an undercover policeman bought five grams of a suspicious substance for USD 15,000 last week.
The police are still looking for four other people linked to the investigation.
