At least six rangers in DR Congo's Virunga national park, famous for its mountain gorillas, were killed Sunday in an attack officials blamed on a militia group.

The UNESCO World Heritage site is caught up in persistent unrest in the eastern North Kivu province, where a plethora of armed groups are battling for control of rich mineral deposits.

"Mai-Mai (militia) carried out an ambush at Nyamitwitwi. The provisional toll is six park rangers killed along with two Mai-Mai," local government delegate Alphonse Kambale told AFP.

Provincial lawmaker Elie Nzaghani confirmed the tally from Nyamitwitwi in Rutshuru province.

"We confirm that a group of armed men attacked our positions in the region of Nyamitwitwi, a central sector of the park in the territory of Rutshuru" in North Kivu province, the park's spokesman Olivier Mukisya told AFP by email.

Mukisya said six rangers were killed and another was seriously injured in the attack around 9:30 am.

Virunga park, created in 1925, covers some 7,800 square kilometres (3,000 square miles) and is home to about a quarter of the world's population of critically endangered mountain gorillas.

Nearly 700 armed rangers work in Virunga where sources say at least 200 have paid with their lives in attacks going back more than a decade.

Various rival armed groups have repeatedly clashed over land and resources and stoked tensions in North Kivu, which like the rest of eastern DR Congo has been riven by decades of conflict.

Mai-Mai militia groups have been accused of killing hundreds of civilians over the years.

Mai-Mai (the word comes from the Swahili for water) sprinkle themselves with water before going into combat in the belief it affords them protection.