Congolese rangers on Tuesday began searching the dense Virunga jungle for six families of critically endangered mountain gorillas who have not been spotted since fighting erupted three months ago.

The regular army has been battling a militia led a renegade general in the eastern Democratic Republic of Congo, where lies part of the Virunga Massif that is home to the world's largest community of mountain gorillas.

The park's director Emmanuel de Merode said in a statement that the army and the so-called M23 rebels had allowed the rangers to launch search operations for the missing primates in rebel-held territory.

"On Tuesday 24 July, a team of 45 rangers will begin a multi-day operation to find and monitor the condition of six mountain gorilla families, some which have not been seen for over 10 weeks," the statement said.

"We are delighted and relieved that all sides in the conflict have recognised the need to protect Congo's only mountain gorillas," de Merode said.

The Virunga volcanoes conservation area straddles DR Congo, Rwanda and Uganda and is home to 480 of the world's 790 remaining mountain gorillas. Their cause was made famous by US zoologist Dian Fossey, who was murdered in 1985.

The danger of extinction facing the mountain gorillas, whose natural habitat is threatened by expanding human settlements, is increased by chronic conflict and poaching.

"After locating the gorilla families, the park's gorilla monitoring teams will individually identify each member of the family," the statement said.

"Their health status will also be assessed as mountain gorillas are particularly vulnerable to disease," it added.

Former rebels named after the failed March 23, 2009 peace deal which saw them integrate the Congolese army defected this year and regrouped in the Virunga before launching an attack on towns in the eastern Nord-Kivu region.

With Kinshasa and Kigali trading accusations of backing eachother's rebels and weeks of conflict displacing hundreds of thousands of civilians since April, DR Congo and Rwanda agreed to the principle of an international force monitoring their border.