Major General Scott Sherman, who leads Task Force 51, said more than 4,000 National Guard troops and 700 Marines are part of a security effort in Los Angeles, where demonstrations have turned violent at times.
An additional 2,000 Guard members are set to deploy on Thursday to support federal building protection.
Sherman declined to say when the Marines might be sent into the city but confirmed all personnel receive specialised training in managing unrest, with further instruction for those supporting immigration raids.