The attack follows the death of 12 Congolese soldiers and seven UN peacekeepers in clashes with militias earlier this week in Democratic Republic of Congo's Ebola-hit east.
Mortar bombs were fired at a UN peacekeeping base and gunfire could be heard on Friday in the Democratic Republic of Congo's eastern city of Beni, an area which has seen a surge in fighting with rebel groups, two sources said.
The attack follows the death of 12 Congolese soldiers and seven UN peacekeepers in clashes with militias earlier this week.
The casualties, incurred during a joint operation against the Ugandan group Allied Democratic Forces (ADF) on Wednesday, make this week one of the deadliest for troops in DR Congo's volatile eastern borderlands since a rebel attack in early 2018.
Congolese army spokesman Mak Hazukay said the army was monitoring the situation in Beni and had imposed a curfew on part of the city.
The African country's volatile east is home to many armed groups vying for control of the mineral-rich region, and the ADF and Mai-Mai rebel groups are especially active in the Beni area.
Congolese military forces were battling militants in the Beni district of Mayangose, Hazukay said, and civilians were "formally banned" from travelling there.
Earlier on Friday, a UN source told Reuters up to 50 soldiers of DR Congo were wounded in the joint operation.
The deaths of the UN peacekeepers, six from Malawi and one from Tanzania, were reported by the United Nations on Thursday.
Eastern DR Congo has been plagued by banditry and armed insurrections for more than two decades since the fall of military ruler Mobutu Sese Seko, but the past year has seen a surge in violence around the North Kivu region.
The insecurity is hampering international efforts to contain an Ebola epidemic, the worst in DR Congo's history, that has infected over 300 people and killed two-thirds of them since July.