NGOs are calling into question the mandate of UN troops in the DRC.
A new UN intervention brigade will be used for the first time to help the Democratic Republic of the Congo (DRC) army set up a "security zone" in the city, the UN said.
A statement by the UN mission in the DRC, Monusco, gave M23 rebels in Goma until 4pm (8pm GMT) on Thursday "to hand in their weapon to a Monusco base" and join a demobilisation programme.
After then, "they will be considered an imminent threat of physical violence to civilians and Monusco will take all necessary measures to disarm them, including by the use of force in accordance with its mandate and rules of engagement".
The UN-proposed security zone includes Goma and its northern suburbs. The M23 launched a new offensive against the DRC army outside Goma on July 14.
"The M23 has used indiscriminate and indirect fire, including by heavy weapons, resulting in civilian casualties," Monusco said.
"The M23 has also targeted UN installations with its fire. The security zone will push these indirect fire threats out of range of Goma. The security zone may be expanded and repeated elsewhere, where it is needed."
UN experts and the DRC government have said Rwanda has supplied troops and military aid to the M23, allegations denied by Kigali.
The United States last week called on Rwanda to end its backing of the rebel forces.
South African involvement
South Africa sent troops to the DRC in April 2013 as part of Monusco.
The Security Council unanimously adopted in late March a resolution establishing the so-called intervention brigade as part of the existing 20 000-strong UN force in th DRC. It is the first time the United Nations has created such a unit within a traditional peacekeeping force.
It was revealed in March 2013, however, that some of the M23 rebels were former trainees of the South African Defence Force (SANDF).
Edward Xolisa Makaya, chief director for southern Africa at the international relations and cooperation department told the South African parliamentary oversight committee in March that over the years, South Africa was "very present" in the military training of the DRC's troops.
SANDF trained three military battalions over the years and that police trained several officers in the DRC.
The DRC's army is fighting M23 rebels in a conflict that has dragged Congo's east back into war and displaced more than half a million people. – AFP, Reuters