The U.S. Justice Department said on Tuesday it is "disappointed" by a South Korean court's rejection to an extradition request for a man convicted of running one of the world's biggest child porn sites.

Acting U.S. Attorney Michael Sherwin of Washington, D.C., issued the position in response to a KBS query about the Seoul High Court's decision on Monday.

Sherwin reportedly said the U.S. was disappointed by the court's denial of extradition in this case against one of the most dangerous child sexual exploitation offenders in the world, whose actions deeply impacted citizens of the United States.

He added that despite the court's decision, the U.S. appreciated the efforts of the South Korean Justice Ministry, adding the U.S. will continue to work with the ministry and other international partners to combat online transnational crime that harms children. 

The court on Monday refused an extradition request by the Department of Justice for Son Jong-woo, the operator of a South Korea-based dark web child pornography site that sold videos for digital cash around the world. 

Son finished serving an 18-month prison term in April, but was taken back into custody pending a decision on his extradition. He was released on Monday after the court's decision.