The positive test has also put Norway's bronze team showjumping medal in jeopardy.
"I know that we are innocent, and I will do what I can to shed light on this case," Hansen said.
Hansen said no-one had "administered any kind of doping substance to Camiro." He called the doping charges "absurd."
Camiro, owned by Norwegian millionaire Kjell Christian Ulrichsen, tested positive for capsaicin.
Capsaicin is used in products to prevent horses chewing wood and other surfaces. A Swedish publication reported that the substance had been found in a spray used by Hansen's stable to spray rugs to prevent horses chewing or biting them.
Camiro was drug tested on arrival in Hong Kong in the FEI's pre-event testing programme, and tested negative.
A hearing concerning Camiro - and three other Olympic showjumpers who also returned positive tests - will take place next month.