The United States imposed sanctions on Monday on a Myanmar warlord, his two sons and the militia he leads, for facilitating online scams, human trafficking and cross-border smuggling, the Treasury Department said.

The Treasury said the warlord, Saw Chit Thu, is a central figure in a network of illicit and highly lucrative internet scam operations targeting Americans. Hundreds of thousands of people have been trafficked by criminal gangs across Southeast Asia in recent years and forced to work in the scam operations, according to the United Nations.

The move puts financial sanctions on Saw Chit Thu, the Karen National Army that he heads, and his two sons, Saw Htoo Eh Moo and Saw Chit Chit, the department said in a statement, freezing any U.S. assets they may hold and generally barring Americans from doing business with them.