Rangers said heavy weapons fire broke out again on Sunday after an overnight lull.

"Right now as we are speaking, the fighting is going on inside the park ... where the gorillas live. The situation is not good," Norbert Mushenzi, director of Virunga's southern sector, told Reuters by phone.

Nkunda first led a revolt in 2004 but signed a short-lived peace deal in January. He says he is fighting to protect the Tutsi minority in Congo against attacks by Rwandan Hutu rebels, whom he says are backed by Congo's President Joseph Kabila.

His fighters in August abandoned the mixed national army brigades they had joined as part of the January peace deal and have since occupied large swathes of Virunga, forcing conservationists to abandon the park.

The latest fighting forced rangers to evacuate computers and communications equipment from a ranger station in the town of Rumangabo, fearing any further rebel advance could cut them off from the provincial capital Goma, 35 km (22 miles) to the south.

At least nine gorillas have been killed in Congo since the beginning of the year, including two slain and eaten by Nkunda loyalists in January. Of a total population of just 700 worldwide, about 380 mountain gorillas live in eastern Congo.

Conservationists say their fate is now in Nkunda's hands.

An informal UN-brokered ceasefire last month had helped to end full-scale fighting in North Kivu, although intermittent skirmishes have continued between Nkunda's fighters, government forces, local militia and rebels from neighbouring Rwanda.

Congo's army claimed to have killed 35 Nkunda loyalists near the town of Ngungu, some 25 km (16 miles) west of Goma, on Thursday. A rebel commander denied the death toll.

Army officials and the country's UN peacekeeping mission, (MONUC) reported more fighting near Ngungu early on Sunday but had no details on casualties.

General Vainqueur Mayala, the army's top commander in North Kivu, said his forces had pushed back attacks on Sunday.

"We repelled them. They attacked us everywhere. They are trying to generalise this," he told Reuters.