Heavy fighting in eastern Congo has driven at least 1,700 people from a refugee camp, the U.N. said Tuesday, and an aid group said a team of its medical workers has been trapped in a nearby hospital.

The fighting resumed late Monday night in the eastern villages of Tongo and Nyanzale, said Lt. Col. Jean-Paul Dietrich, a spokesman for the U.N. mission in Congo. The fighting pitted Congo's army against the National Congress for the Defense of the People, or CNDP, a rebel group claiming to be protecting the area's Tutsi minority.

He said at least 1,700 people were forced to flee from the refugee camp in Tongo.

Doctors Without Borders said a team of its workers has been trapped since Monday night in the hospital in the village of Mweso, near Tongo because of fighting in the surrounding hills.

The fighting there has been going on sporadically for about a week, but intensified on Monday, said Colette Gadenne, a regional head for the aid group.

Workers reported hearing heavy arms fire very nearby, she said.

"This morning they could hear the bombings and rocket launchers. And they could hear the gunshots last night," Gadenne said Tuesday.

It is too dangerous for the group's 25 medical workers, five of them foreign staff, to return to their homes in Mweso, she said. About 30 government staff are sequestered in the facility, and 68 patients.

Rebels led by the rebel CNDP's Laurent Nkunda have fought the army sporadically in the region for years. But clashes have intensified in recent months and the U.N. says more than 100,000 people have been displaced since August.