Six park rangers were killed on Sunday morning in an attack at the famous Virunga National Park in the Democratic Republic of Congo.
Officials have blamed the attack on a militia group known as Mai-Mai, one of many that operate in the region.
The rangers were ambushed while on foot patrol inside the Unesco World Heritage park, a spokesman told the BBC.
Staff working in Africa’s oldest nature reserve often come under attack. In April last year 13 rangers were killed in a rebel ambush.
A statement from the park said preliminary investigations suggested the rangers “were taken by surprise and had no opportunity to defend themselves” during the attack.
A local government delegate, Alphonse Kambale, told AFP news agency that two Mai-Mai militants had also been killed.
Boasting Africa’s most diverse wildlife, including about a quarter of the world’s remaining mountain gorillas, Virunga, which stretches across 7,800 sq km is one of the most dangerous parks on the continent.
Around 2,000 armed fighters roam Virunga and its surrounding areas. They belong to numerous different rebel groups, who battle for control of the region’s rich resources.
They fish illegally, slaughter the park’s animals, fell its trees – and kill, rape and abduct locals and foreign tourists alike.
Nearly 700 armed rangers work in Virunga. At least 200 have been killed in attacks.