The Justice Department unsealed charges Thursday against more than two dozen North Korean individuals accused of making at least 2.5 billion in illicit payments linked to the country's nuclear weapons and missile program.

The case, filed in federal court in Washington, is believed to be the largest criminal enforcement action ever brought against North Korea.

The 33 defendants include executives of North Korea's state-owned bank, Foreign Trade Bank, which in 2013 was added to a Treasury Department list of sanctioned institutions and cut off from the U.S. financial system.

According to the indictment, the bank officials one of whom had served in North Korea's primary intelligence bureau set up branches in countries around the world, including Thailand, Russia and Kuwait, and used more than 250 front companies to process U.S. dollar payments to further the country's nuclear proliferation program.

Five of the defendants are Chinese citizens who operated covert branches in either China or Libya.

Through this indictment, the United States has signified its commitment to hampering North Korea's ability to illegally access the U.S. financial system and limit its ability to use proceeds from illicit actions to enhance its illegal WMD and ballistic missile programs," acting U.S. Attorney Michael Sherwin said in a statement.

The prosecution underscores ongoing concerns about sanctions violations by North Korea.

Last month, United Nations experts recommended blacklisting 14 vessels for violating sanctions against North Korea, accusing the country in a report of increasing illegal coal exports and imports of petroleum products and continuing with cyber attacks on financial institutions and cryptocurrency exchanges to gain illicit revenue.

The U.S. has seized about 63 million from the scheme since 2015, according to the indictment.

It was not immediately clear whether any of the defendants had lawyers.