Eastern Democratic Republic of Congo's restive North Kivu province is said to be quiet Friday after the worst outbreak of violence there in months. As VOA Correspondent Alisha Ryu reports from our East Africa Bureau in Nairobi, U.N. officials are working to maintain a fragile cease-fire signed between the government in Congo Kinshasa and Tutsi rebels.

The military spokesman for the U.N. Mission in Congo Kinshasa, Lieutenant Colonel Jean-Paul Dietrich, tells VOA that although the fighting between government forces and rebels has ceased, the situation in the north of the provincial capital Goma remains extremely tense.

The two sides exchanged heavy machine-gun and mortar fire for eight hours in the Rutshuru Territory in North Kivu on Thursday, causing thousands of civilians to flee and an unknown number of casualties.

"Negotiations went on at the highest level in Kinshasa between the U.N. and the Ministry of Defense, between our military force commander and the Chief of Staff of the Armed Forces, and also in Goma with representatives of the CNDP. But, definitely, the situation is tense," said Dietrich.

The rebel CNDP group is led by ethnic Tutsi Laurent Nkunda, who is believed to have ties to the government in neighboring Rwanda. After Kinshasa's broader civil war ended in 2002, Nkunda began an armed rebellion in 2006, claiming that he was fighting for minority ethnic Tutsis in eastern Congo and their protection from ethnic Hutus responsible for carrying out genocide against Tutsis in Rwanda in 1994.

In January, Nkunda and the government signed a cease-fire that had restored some calm after major clashes devastated North Kivu province late last year.

For the past 12 months, the rebels have occupied the southern area of Congo's famed Virunga National Park, home to about 380 rare mountain gorillas. Following Thursday's clashes, Congolese wildlife authorities expressed concern about the status of the gorillas after mortars exploded inside the park.

Dietrich says he does not know what specific incident triggered the latest violence.

"That is still not clear, and why," said Dietrich. "But there was a lot of tension in the air already for many days and it needed just some small incident, which could blow off the tension and now it has happened. We really regret it, but all of the parties have expressed its willingness to come back to the negotiating table. Even CNDP said this kind of incident is not in their interest at all."

North and South Kivu provinces are rich in minerals and other natural resources and the fighting in the north is believed to be tied to rebel attempts to expand the territory under their control and government efforts to stop them.

The United Nations estimates about 850,000 residents in North Kivu have been displaced by fighting since December, 2006.