Mexican authorities say they have launched an investigation into the castration of a black bear who became famous after appearing in a selfie taken by a fearless hiker.

The animal made international headlines when a woman snapped a photo of it standing with its face just behind her head in an ecological park in northern Mexico.

The 96-kilogram bear then ambled off, leaving her unharmed. It also approached another woman in a nearby area without hurting her.

The bear was captured last week while sleeping outside a house and transferred to a veterinary faculty at a university in the northern state of Nuevo Leon for a routine check-up.

Once there, a wildlife laboratory at the faculty decided that it was necessary to castrate the bear due to its "erratic behaviour," wildlife protection authority Profepa said Sunday in a statement.

It said the bear was feeding in an urban area.

The castration was authorized by a senior Profepa official who deemed it necessary to reduce the risk of the animal fighting with other bears and to avoid the reproduction of two subspecies.

Profepa, which is overseeing the probe, said Sunday that it had requested documents to justify the operation on the bear, which was later released in another part of northern Mexico.