Five park rangers were killed in a joint operation with the army to rescue an American journalist and three park rangers, who went missing in a wildlife reserve in Congo, a local official said on Sunday.

Gunmen attacked the group late on Friday in the Okapi Wildlife Reserve in eastern Congo, which is also known as Congo-Kinshasa. Some others in the group, including two Dutch journalists, escaped.

Mambasa administrator Alfred Bongwalanga said security forces and park rangers had launched a rescue operation that located the missing members of the group. It was not immediately clear how the rangers were killed.

"There are five dead. They are all park rangers who were involved in the operation. They had been backing the army," he told Reuters by telephone.

Attack blamed on local militia

Cosma Wilungula, head of Congo's park service, confirmed the journalist and rangers had been rescued from a group of Mai Mai militia fighters involved in mining gold inside the reserve.

While he said two rangers had been killed in the initial attack he had no information on casualties during the rescue.

"It's a zone that's not secure for us.... They were heavily armed and the rangers found themselves in an inferior position," Wilungula said, referring to the initial attack.

Eastern Congo has been the theatre of numerous wars and uprisings over the last two decades, and rebels, militia fighters and bandits still present a security risk in many areas.

Park rangers trying to protect dwindling populations of elephants and gorillas often clash with poachers and other armed groups who exploit minerals, wildlife and other resources.

Later on Sunday, Congo's Virunga National Park said that one of its rangers had died following an ambush by Mai Mai militia in an area of the park west of Lake Edward.