Twenty people have been indicted for their alleged involvement in an international money laundering organization that used banks in Massachusetts and other locations to launder more than $6 million in drug trafficking proceeds.

The Boston U.S. Attorney Rachel Rollins’ office said in a statement this week that $1 million has been seized from corporate bank accounts and other investigative activity.

According to the statement, law enforcement began an investigation in 2016 into a money laundering organization located primarily in Barranquilla, Colombia. During a five-year investigation, the organization allegedly laundered over $6 million in drug proceeds through intermediary banks in the U.S., including banks in Massachusetts. Banks in the Caribbean and Europe were also allegedly used.

Prosecutors allege that defendants used an illegal currency exchange process called the Colombian Black Market Peso Exchange to conceal drug trafficking activity while also evading currency exchange requirements in the U.S. and Colombia. The Rollins’ office’s statement said that defendants allegedly had roles within the money laundering organization that included drug suppliers, peso brokers, money couriers, and business owners, also known as dollar purchasers.

According to Rollins’ office, Colombian drug trafficking organizations with drug proceeds generated in the U.S. use third parties – generally referred to as “peso brokers” based in Colombia – who agree to exchange Colombian pesos they control for the drug supplier’s dollar proceeds.

Peso brokers then use money couriers in the United States and elsewhere, the statement said, to physically secure the drug proceeds and transfer the proceeds into the U.S. banking system.

Peso brokers avoid detection by depositing the drug proceeds into bank accounts in company or individual names intended to appear as legitimate business activity. They also use multiple small deposits into different bank accounts, the statement said, which are then consolidated into larger accounts. Court documents did not identify the banks used in the scheme.

The proceeds in U.S. banks are then purchased by individuals or companies in Colombia seeking to exchange pesos for U.S. dollars at a favorable exchange rate and in a manner that avoids currency exchange and income reporting requirements, the U.S. attorney’s office said. The proceeds, which are transferred at the direction of the purchaser, could end up in bank accounts of individuals or companies who appear to have no direct involvement in drug trafficking crimes, the statement said.

Six defendants were arrested this week, according to the statement, with three arrests happening in Florida and the other three arrests taking place in Jamaica at the request of the U.S. Last month, 12 defendants were arrested in Columbia, and one was arrested in Orlando, Florida. Information on another defendant has been redacted. The U.S. attorney’s office said the U.S. would seek extradition of the Colombian and Jamaican defendants to Massachusetts.