Rebels have attacked a nature reserve in eastern Democratic Republic of Congo, killing a ranger and critically injuring three, say conservationists.
Some 200 Mai Mai militia fighters attacked three observation posts in the Virunga National Park.
They are threatening to kill a rare group of mountain gorillas if the authorities come after them.
WildlifeDirect director Emmanuel de Merode said the Mai Mai attack may be a reprisal for a government clampdown.
"Our understanding is that this was a deliberate attack on the Congolese wildlife authorities," he told the BBC's Focus on Africa.
Almost 100 rangers in Virunga have died protecting the gorillas
Hutu rebels and Mai Mai fighters have sought sanctuary in recent years in the park, during a long conflict that has led to some four million deaths.
But there has been a recent attempt to drive out and demobilise the remaining militias in the east.
Mr Merode said there were two important gorilla populations who have been under attack since the beginning of the war.
"The efforts of the Congolese rangers to protect these have been quite successful but at a huge human cost."
"Over 97 rangers have been killed in Virunga National Park since the war started in 1996," he said.