Rwanda handed over six orphaned gorillas to the Democratic Republic of Congo after poachers smuggled them out of the country to sell as exotic pets, or for consumption as bush meat.
Poaching has decimated populations of chimpanzees, gorillas and forest elephants in the jungles of west and central Africa and regional governments have vowed to step up efforts to stop trafficking.
Mountain gorillas are listed as critically endangered, with about 680 surviving in the wild, all in central Africa.
Rwandan authorities said on Sunday they had rescued the gorillas, aged between 5 and 8 years old, from traffickers in various parts of the country.
Officials have detained six Rwandan and Congolese men whom they believe are part of a wider criminal ring. Gorillas are caught and sold for thousands of dollars on the world market as exotic pets, or killed and sold locally as a delicacy.
"Because the countries are working together we managed to reduce that (poaching) .... we are able to minimize that but it is still a challenge," said Rwanda's director general of tourism and parks, Rica Rugambwa, on the Rwandan-Congolese border.
The gorillas were flown from there to a research center and were then due to be released into the wild.
The rare mountain gorillas are found in a Ugandan national park or in the Virunga Volcano Region, which straddles the borders of Rwanda, Uganda and Congo.
The WWF says more than 100,000 people live near the forests where they are found. Poaching, capture for illegal wildlife trade, as well as people's need for land to grow food has reduced the mammals' forest habitat to "virtual islands in the middle of human settlements," WWF says.
Congo's mountain gorillas have also weathered years of warfare in the country's east. Dozens of rangers have been killed trying to protect the area's five national parks from poachers and armed groups.
"We came to finish the war and security is coming slowly," Congolese Environment Minister Chantal Kambibi said. "We will try to protect them properly."
