DAR ES SALAAM, Tanzania — Authorities in northern Tanzania suspect poison may have caused the deaths of 10 lions inside a protected conservation area and UNESCO World Heritage site.

The lions were discovered Friday in the Ndutu part of the Ngorongoro Conservation Area, according to the conservation group overseeing the site.

“Preliminary findings suggest the animals may have died after ingesting poison,” the Ngorongoro Conservation Area Authority said in a statement.

An investigation is underway to establish the definitive cause of the deaths inside the area where wildlife including lions, elephants and black rhinos live in proximity with semi-nomadic Maasai pastoralists.

The International Union for Conservation of Nature classifies lions as vulnerable and says their numbers are declining. Threats facing the species include habitat loss, declining prey populations and human-wildlife conflict.