The U.N. peacekeeping mission in DRC said it was supporting efforts by the Congolese military to fight off rebels from the March 23 Movement. It said three peacekeepers were injured by mortar shells fired from M23 positions during fighting last week.
The mission said at least three civilians were killed by mortar shells fired near camps for the internally displaced in Goma, the provincial capital of North Kivu in eastern DRC.
M23 captured Goma last year, but retreated later under U.N. observation. U.N. special envoy to DRC Martin Kobler said he's lost his patience with the rebel movement.
"No act of this nature by the M23 will be tolerated and any attack on the civil population and the United Nations constitutes a war crime," he said in a statement Saturday.
M23 leader Bosco Ntaganda surrendered to the International Criminal Court early this year to face war crimes charges. Rwanda is suspected of backing the movement, an allegation the government denies
U.S. State Department spokesman Marie Harf said Saturday the conflict caught Washington's attention after the United Nations reported M23 rebels fired into Rwandan territory.
"We call on the M23 to immediately end the hostilities, lay down their arms, and disband," she said in a statement.