At least 17 people, including 12 rangers were killed on Friday in an attack in Virunga National Park, a Unesco World Heritage site in the restive east of the Democratic Republic of Congo, an official said.
It was one of the deadliest attacks in the park, Africa's oldest and most biologically diverse protected area.
Besides the 12 park rangers, a driver and four other civilians were killed in the attack in Goma, for which no person or group has claimed responsibility, the governor of the Nord Kivu province said in a statement.
"Others were injured, including some who are fighting for their lives," the park management added in another a statement.
It said that civilians were the apparent target of the attack.
The guards were killed "while coming to help a civilian vehicle which had come under fire by the assailants," the statement said.
Virunga is a UNESCO-listed site which is spread over 7,800 square kilometres (3,000 square miles) over the borders of DR Congo, Rwanda and Uganda.
It is home to a world-famous population of mountain gorillas but has been hit by rising instability and violence.
Inaugurated in 1925, the park has witnessed repeated attacks by rebel groups, militias and poachers.
A total of 176 of its rangers have been killed in the last 20 years.
Visits to the park have been suspended since March 19 for at least 30 days in DR Congo's bid to halt the new coronavirus pandemic.
The park banned visitors between May 2018 to the start of last year after two British tourists were kidnapped there. They were later released but a ranger was killed during the abduction.
In another attack, in the northeast Ituri region on on Thursday, seven civilians were killed by militiamen, army spokesman Jules Ngondo told AFP.
"The army neutralised ten assailants," he added.
UN radio station Okapi put Thursday's toll at 13 civilians dead.
Both sources blamed that attack on members of CODECO - whose official name is Cooperative for the Development of Congo - an armed political-religious sect in Ituri drawn from the Lendu ethnic group.
Last month the army announced it had killed COECO head Ngudjolo.
Tens of thousands were killed between 1999 and 2003. According to the UN, most victims were targeted because they were Hema.
The conflict has reignited in recent years.
More than 700 people have been killed in Ituri since late 2017, a UN report said in January, adding that some of deaths might constitute a crime against humanity.