BUCHAREST (Reuters) - Romanian police seized 2.5 tons of cocaine worth at least 600 million euros ($667.20 million) hidden in Colombian banana containers that arrived in the Black Sea port of Constanta, the country's biggest ever drug bust.

Four Lithuanians and one Colombian were arrested in Romania after a six-month-long operation involving undercover agents and back-up from U.S. authorities, the Balkan nation's anti-mafia police said in a statement on Friday.

Traffickers had arranged for the cocaine, which had arrived from Colombia last week, to be transferred to trucks, concealed among construction materials, and transported to the Netherlands, it said.

A man with Spanish and Dutch citizenship was also arrested in Spain in connection with the cocaine shipment.

(Reporting by Radu Marinas; editing by Mark Heinrich)