Ten executives and employees from four cryptocurrency trading firms were charged Monday in federal court in Oakland in connection with alleged schemes to inflate digital token prices and trading activity through fraudulent “wash trading,” federal prosecutors said.

Three defendants — including two chief executive officers — were arrested in Singapore and appeared in federal court following their extradition to the United States, the U.S. Attorney’s Office for the Northern District of California said. Two others have already pleaded guilty and been sentenced.

Employees from the firms Gotbit, Vortex, Contrarian and Antier were charged in three separate federal indictments alleging they carried out “wash trading” schemes designed to create…