According to CNN, four more peacekeepers are missing after the attack in Beni, the United Nations said in a news release. The peacekeepers killed were from Tanzania, it said.
A day earlier, a U.N. helicopter carrying the mission's commander came under fire from unknown gunmen. It landed safely.
"The U.N. remains committed to taking all necessary actions to protect civilians and neutralize armed groups in eastern DRC," the world body said in a statement after the ambush.
A U.N. team is on the ground supporting the local army as it battles Ugandan rebels in the restive eastern Congo. Beni is in the northeastern part of the vast country, not far from the border with Uganda.CNN reports.
The Uganda-based Allied Democratic Forces has attacked villages in eastern Congo and killed residents in recent months, according to the United Nations.
Eastern Congo is still trying to get back on its feet after a conflict left millions dead from 1998 to 2003.
As a result of the instability, armed militants run amok in the region, which is rich in gold and diamonds.