"There has to be a full restoration both of the institutions of governance and justice as well as the full restoration of a duly democratically elected civilian government," the senior State Department official told journalists.
It follows a recent visit by Daniel Russel, the most senior US official to travel to the kingdom since Thai generals imposed martial law and took over in a coup last May.
The United States strongly condemned the coup at the time, with chief diplomat John Kerry calling for a return to civilian rule via democratic elections.