The president of the Rwandan Hutu rebel group known as the FDLR, Victor Byiringiro, said the move was aimed at contributing to peace in the region.
Congo's government spokesman said today's ceremony was a step in the right direction but that the military is still waiting for more than 1,400 fighters to surrender.
The UN Mission in Congo said it received reports that the FDLR "has expressed its intention to begin the surrender process in South Kivu in 72 hours," UN spokesman Stephane Dujarric told reporters at UN headquarters in New York.
"It reports that all resources have been mobilized on a priority basis for a swift and well-organised transfer of ex-combatants to transit camps and later on to their final destination.
The FDLR has been active in eastern Congo ever since the 1994 genocide in neighboring Rwanda, when perpetrators of the killings fled into Congo.
Eastern Congo is home to a myriad of armed groups vying for control in the mineral-rich region.