The rebel March 23 Movement seized control over parts of eastern DRC last year. Former M23 leader Bosco Ntaganda surrendered to the International Criminal Court, where he's the subject of two arrest warrants for war crimes committed in DRC.
The State Department said it was concerned about the security situation in the DRC.
"Armed groups, bandits, and elements of the Congolese military remain security concerns in eastern and northeastern DRC," a State Department announcement said.
The U.N. mission in DRC said about 1,500 civilians sought refuge near a peacekeeping base in eastern DRC in early April. They fled the area near the Rwandan border following clashes between Congolese and rebel forces.
The U.N. Security Council backed a special unit within the peacekeeping mission that would have combat duties.
Rights group said the intervention brigade would raise the risk of reprisal attacks.
"Although the rebels withdrew from (North Kivu provincial capital) Goma in December 2012, the security and political situation in Goma and North Kivu remains tense and fragile," the State Department said.