"It's true, one third of Akagera National Park has burnt over the past week…but the fires are under control as I am speaking," park warden David Mugisha said on Thursday.
Akagera is a haven for wildlife in overcrowded Rwanda, where over 8 million people are squeezed into just 26,300 sq km and deforestation is already widespread.
The sprawling 900 sq km park in the east of the country is home to elephants, giraffes, zebra and various species of antelope and monkey.
Mugisha said poachers lit the fires to scatter animals and then set snares to catch them should they return to feed on vegetation that grows back.
"We are very much concerned…it's very damaging and very abrupt for the biodiversity of the park," he said.
He said the poachers were both commercial hunters working in the bush-meat trade and subsistence hunters trying to feed themselves.
Mugisha said no arrests had been made but patrols in the park were being increased.
The 'catastrophe' in the Rwandan park comes in the wake of a warning from the conservation group WWF International, stating that illegal settlers have destroyed huge areas of mountain gorilla habitat in neighbouring Congo.