Four people were killed and two seriously injured in a clash between national park rangers and suspected Rwandan rebels in the war-torn Democratic Republic of Congo, the park said.
The Virunga national park, home to DR Congo's only population of endangered mountain gorillas, said one of its rangers died in a battle on Saturday morning that also claimed the lives of three rebel fighters.
Two other guards were wounded and one rebel was captured.
Virunga said in a statement that the Sunday clash was with the FDLR, a Rwandan rebel group that includes the remnants of the militia who carried out the 1994 genocide.
"The attack is thought to have been carried out in retaliation against the rangers' efforts to prevent the militias from regaining control of an area close to the habitat of the critically endangered mountain gorillas," the park said.
Virunga national park, a UNESCO world heritage site, was founded in 1925, making it Africa's oldest national park.
It is the most environmentally diverse area on the African continent, home to thousands of rhinos and 200 endangered mountain gorillas.