Authorities in Tanzania plan an auction of 3.5 tons of hippo teeth next week, drawing criticism from conservation groups who say the sale could encourage increased killing of the species for its body parts.

Tanzanian wildlife authorities say licensed dealers on Monday can bid for the 12,500 pieces of hippo teeth at the tourism and natural resources ministry in Dar es Salaam.

The WWF conservation group said Friday that many hippo populations face pressure from hunting for their ivory and meat and that it is "disappointed to see auctions such as this taking place."

An international "red list" of endangered species classifies the hippo as vulnerable. It estimates there are up to 130,000 hippos in sub-Saharan Africa.

Hippo teeth are carved into ornaments for sale in parts of Asia.