Conservationists have expressed concern over the "senseless and tragic" killing of four mountain gorillas in the Democratic Republic of Congo.
The bodies of three females and one male were discovered by rangers earlier this week in the Virunga National Park.
Officials said the "executions" were not the work of poachers because they would have taken the bodies.
Since January, seven of the large apes in the region have been shot dead.
"This is a senseless and tragic loss of some of the world's most endangered and beloved animals," said Deo Kujirakwinja of the Wildlife Conservation Society's (WCS) Congo programme.
"This area must be immediately secured or we stand to lose an entire population of these animals," he added.
The four animals belonged to a group of 12 gorillas, known to researchers as the Rugendo family, which was often visited by tourists.
Because poachers would have sold the bodies as food or trophies, conservationists think the apes were killed by a group that was trying to scare wardens out of the park.
The WCS said the protected area was coming under increasing pressure from "outside exploitation", including the charcoal trade.
"Whatever the motive underlying this tragedy, the gorillas are helpless pawns in a feud between individuals," said Mark Rose, chief executive of Fauna and Flora International.
"We are deeply concerned about this incident, which follows more than 20 years of successful collaboration for mountain gorilla conservation."
A census carried out in 2004 estimated that 380 gorillas, more than half of the world's population, lived in the national park and surrounding Virunga volcanoes region.
The latest killings take the number of shootings in the area to seven. Earlier this year, two silverback male gorillas were shot dead in the same area of the park, while a female was killed in May.