The poachers, who attacked just before nightfall last Thursday, sought to capture and sell baby gorillas. They made off with one baby gorilla after killing two females.

Officials said it was the first time since 1985 that poachers had attacked the gorillas for this purpose.

Two men are being held in custody over the killings but officials believe they are part of a larger criminal ring.

"This cannot be an operation mounted by a couple of guys," said Solange Katarebe of the Rwandan Tourism Authority.

The gorillas have become Rwanda's biggest tourist attraction, living in bamboo thickets on the slopes of the Virunga mountains which straddle northwestern Rwanda, the Democratic Republic of Congo and Uganda.

They move freely across national boundaries and experts say that it is difficult to ascertain the total population of the mountain gorilla for the three countries.

Tourist pay around $250 each to spend an hour with the animals. It was the work of the late American primatologist Diane Fossey in the 1970s and 80s that first brought the gorillas to the attention of the general public.

In Rwanda the animals are heavily guarded and viewed as a national treasure.

While the more numerous western lowland gorilla found in the Congo basin is often killed and eaten as bush meat in the Republic of Congo and Gabon, eating gorilla meat in Rwanda and other eastern African countries is regarded as a strong taboo.

Last year a group of Rwandan rebels returning from Congo broke that taboo after several days of wandering hungry in the mountains, by killing and eating two gorillas in Virunga Park.