M23 consists of former rebels integrated into the DRC military who mutinied last year, complaining the government wasn't upholding its commitments to a 2009 peace treaty. The group is accused of committing war crimes and last week fired twice on U.N. helicopters patrolling eastern DRC.
"We call on all parties ... to remain at the negotiating table and to promptly conclude the talks with a final and principled agreement that includes a permanent cessation of hostilities, the immediate disarmament and demobilization of the M23," she said during her regular press conference Monday.
A Tanzanian member of the U.N. peacekeeping force in DRC, known by its French initials MONUSCO, was killed while patrolling alongside the Congolese military in the east of the country last weekend.
The U.N. Security Council issued a statement Monday condemning the attack in the "strongest terms."