A deadline set by UN peacekeepers for rebels in the volatile eastern Democratic Republic of Congo to lay down their weapons passed on Thursday, with the fighters facing force if they fail to disarm.
The M23 rebel group, which launched a fresh offensive against the Congolese army outside the flashpoint city of Goma on July 14, on Wednesday dismissed the ultimatum as irrelevant.
The UN mission in DR Congo, MONUSCO, gave them until 4:00 pm (1400 GMT) on Thursday "to hand in their weapons to a MONUSCO base" and join a demobilisation programme.
"We consider that this measure does not concern us," said M23 chief Bertrand Bisimwa. He said his fighters were not in the region south of Goma where much fighting has taken place recently.
A new UN intervention brigade will be used for the first time to help the DR Congo army set up a "security zone" around the city, the international body said.
If the M23 did not disarm, "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".
A coalition of rights groups, unions and religious associations in North Kivu province, where Goma is located, said Thursday it was losing patience with the UN brigade.
The group issued its own ultimatum, giving the troops one week to act, without giving details of their planned "large-scale" actions if they did not.
"We will push them to act and if not, they can pack their bags," said spokesman Me Omar Kavota.
The UN-proposed security zone includes Goma and its northern suburbs.
The M23, a mainly Tutsi Congolese group founded in 2012, launched a new offensive against the DR Congo army outside Goma on July 14.
Diplomats say fighting in the past two weeks has left hundreds dead.
"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," the statement said.
The M23 is among some 30 armed groups active in North Kivu.
But analyst Fidel Bafilemba of the Enough Project -- dedicated to ending genocide and crimes against humanity -- argued that they were positioned far from the areas specified by the UN force.
"What would make a major difference would be to set a more extended security zone," he said. "But this is perhaps just a beginning.
The new, heavily armed 3,000-strong UN intervention brigade is drawn in roughly equal numbers from Malawi, South Africa and Tanzania.
It joins the 17,000 peacekeepers already deployed in the area with MONUSCO, the stabilisation force.
Its mission is to carry out offensive operations, alone or with Congolese troops, against rebel fighters.
Goma is the capital of North Kivu province, which borders two of DR Congo's eastern neighbours, Rwanda and Uganda.
M23 rebels captured the city on November 20 last year, holding it for 10 days. They left only when leaders from the Great Lakes nations of central Africa promised fresh negotiations, opening the talks in the Ugandan capital Kampala.
UN experts and the DR Congo 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 alleged backing of the rebel forces.
Rwanda and DR Congo are both signatories to a UN-brokered peace and security framework signed in March agreeing not to interfere in each other's affairs.
DR Congo further agreed to reform its security forces and take new efforts to spread government authority.
On Friday, the government in Kinshasa issued arrest warrants for four of M23's leaders it said had taken refuge in Rwanda.
It accused them of "war crimes, crimes against humanity including murder, imprisonment, torture, rape, sexual slavery, ethnic persecution" and several other charges.