Ten lions were found dead in Tanzania’s celebrated Ngorongoro Conservation Area, and wildlife officials suspect poison is to blame, reports Reuters.

The animals were found Friday, and early tests suggest they died after consuming a toxic substance.

The incident underscores long-running tensions between predators and livestock owners in parts of East Africa, where poisoning has repeatedly threatened lions and other large carnivores.

Ngorongoro, a UNESCO World Heritage Site in northern Tanzania, draws tourists from around the world and shelters lions, elephants, buffalo, and endangered black rhinos, Newser has reported.

However, the number of people living in the Ngorongoro region has ballooned from 8,000 in 1960 to about 100,000 today, and related trouble is becoming more frequent, notes AFP.

At least 20 elephants have died since June near the Tanzanian border in Kenya’s Amboseli region from suspected pesticide poisoning, although officials have not determined whether the deaths were deliberate.