The U.S. Treasury Department has frozen more than $40,000 held by blacklisted North Korean officials in recent years, South Korean officials said Tuesday, in the latest sign of pressure on North Korea over its nuclear program.

The Treasury Department froze $40,800 in a total of nine cases from May 2014 to April 2015, the officials said. The U.S.

authorities found out the North Korean funds, which were exposed as financial transactions involving U.S. dollars going through the U.S. financial system.

The U.S. reportedly spent about $432,000 in tracing and freezing the North Korean funds.

The news came just days after the Treasury Department designated North Korea as a "primary money laundering concern" to cut off Pyongyang from the international banking system for its nuclear and missile programs.

The designation came as part of the North Korea Sanctions and Policy Enhancement Act enacted in February to punish the North for conducting its fourth nuclear test in January and a long-range rocket launch the following month in violation of U.N. resolutions. (Yonhap)