PARIS — The scandal over horse meat in the European food chain widened Thursday from a case of mislabeling to one of food safety as public health authorities in Britain said that a powerful equine painkiller, potentially harmful to human health, ‘‘may have entered the food chain’’ in France.

British officials sought to reassure the public that the drug — phenylbutazone, or bute, an anti-inflammatory used commonly on lame horses — was found only in trace amounts in a small number of British horse carcasses. Out of 206 carcasses, eight tested positive for bute, and just six of those carcasses were exported to France.