The UN has given residents of the Democratic Republic of Congo city of Goma 48 hours to disarm, warning force will be used if they fail to do so.
A new 3,000-strong UN intervention brigade is in the area to tackle various rebels, including the M23.
It has been given a mandate to use lethal force against the rebels, who they say have killed civilians in the region surrounding the city of Goma.
Renewed clashes broke out between the rebels and the army earlier this month.
A statement by the UN mission in the DR Congo, Monusco, has given everyone in Goma and surrounding areas until 1400 GMT on Thursday to hand in their weapons to the city's UN base, warning that anyone caught after this would be considered a rebel.
"They will be considered an imminent threat of physical violence to civilians and [UN mission in DR Congo] 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 statement read.
Only soldiers will be allowed to carry weapons, it adds.
The BBC's Maud Jullien in the city says the idea of the new security zone is to establish a clear limit for the M23 - the UN is warning that if they enter this perimeter, the new intervention brigade and the regular Monusco peacekeeping troops will disarm them.
As well as the city, the security zone also includes the airport, the refugee camps and the military bases of both the UN and the army. The M23 do not control any area inside this zone.
Monusco head Lt Gen Carlos Alberto dos Santos Cruz told the BBC it is a "preventive measure" and the security zone is "forbidden" to any armed groups.
The UN accuses M23 rebels of causing civilian casualties with "indiscriminate and indirect fire" in fresh clashes with the army in Mutaho, about 7 km north of Goma on 14 July.
The 3,000-strong intervention brigade is a new departure for the UN to try to stop the M23 rebels, as well as answer the criticism it faced when the rebels managed to occupy Goma for 10 days in November last year, correspondents say.
The UN says up to 70,000 people have been displaced by recent fighting between the rebels and the army, with many fleeing to neighbouring Uganda.
Last week, the US called on Rwanda to stop backing the M23 rebels. UN experts and DR Congo officials say Rwanda has been supplying troops and military aid to the rebels.
Rwanda has dismissed the claims.
"Scapegoating is not going to help DRC," Foreign Minister Louise Mushikiwabo said ahead of a meeting of heads of states in Kenya at the Great Lakes summit which will discuss the unrest in DR Congo.
The M23 rebels, who like Rwanda's leaders are mainly from the Tutsi ethnic group, mutinied and deserted from the Congolese army in April 2012, forcing an estimated 800,000 people from their homes in the ensuing unrest in the mineral-rich region.