UN troops in the Democratic Republic of Congo are taking up positions to support a planned offensive against Hutu rebels in the east after they ignored a deadline to surrender, a UN spokesman said.
The rebels from the Democratic Forces for the Liberation of Rwanda (FDLR) were given until January 2 to give themselves up or face military action.
"The UN mission has pre-positioned its troops and enablers to support offensive operations against the FDLR in keeping with its mandate," said UN spokesman Stephane Dujarric on Monday.
UN mission chief Martin Kobler briefed the UN Security Council earlier Monday on the plan for the 20,000-strong MONUSCO force to support Congolese government troops in their military campaign.
But the United Nations cautioned that military action alone will not lead to the defeat of the Hutu rebels, blamed for a string of brutal attacks in the eastern DR Congo.
"Military operations have the potential to weaken but not to eliminate the FDLR and the military solution needs to be part of a larger comprehensive strategy that includes a number of non-military steps," Dujarric told reporters.
A group of 83 FDLR rebels turned themselves in on Sunday in the face of threatened action, but up to 1,500 others are thought to be still in camps in the remote jungle of the eastern DR Congo.
Hundreds of rebels have given themselves up since the United Nations and regional leaders began putting forward the ultimatum, leaving the hard core rebels to dig in and refuse surrender.
The group includes fighters suspected of having participated in the 1994 Rwandan genocide.
UN and Congolese forces on Monday seized several rebel bases in a separate offensive launched against a Burundi rebel group, the National Liberation Forces (FNL).
A spokesman for MONUSCO in DR Congo said troops taking part in joint operations against FNL fighters in the east of the country had taken several Hutu rebel strongholds.
Lieutenant Colonel Felix-Prosper Basse said the bases were located near the Burundi border in South Kivu.
Asked whether the operation might harm the planned offensive against FDLR, Colonel Patrick Opia, operations commander for Congolese forces (FARDC), said it served as a caution.
"This operation is a warning to FDLR that FARDC and UN forces are determined to hit hard," he said, adding that the operation would last 45 days and could be extended.
UN officials are pushing for the disarming of dozens of rebel and splinter groups after two decades of conflict in the eastern DR Congo, much of it fuelled by the lucrative trade in minerals.
The International Crisis Group warned last month that the "entire stabilization agenda for the eastern provinces was at risk" over the UN's failure to root out the armed groups.