The UN's Office for the Coordination of Humanitarian Affairs (OCHA) said the planned offensive by Congolese and UN forces was likely to cause mass displacement, according to documents cited on Saturday by the news agency Reuters.

Several thousand Hutu rebels ignored a January 2 deadline to surrender. The Security Council reacted on Thursday by authorizing a joint operation by the UN's 20,000-strong force MONUSCO and Congolese government troops.

The UN council's 15 member nations said unanimously that the rebels, who call themselves the Democratic Forces for the Liberation of Rwanda (FDLR), must leave eastern Congo "immediately."

The group, which includes former Hutu soldiers and militiamen blamed for the 1994 genocide in neighboring Rwanda, targeted civilians when the UN staged its last major offensive in eastern Congo in 2009.

Reuters said OCHA "planning documents" warned that a new offensive against the FDLR could again result in "tens of thousands" of civilians being forced to flee their homes.

Capacity to assist doubted

It said spillover from the planned offensive would "quickly overwhelm" DRC Congo's "weak local capacity" to assist civilians, thereby forcing international donors to step in.

A million people were displaced in 2009. The latest OCHA documents listed potential displacements in eastern Congo's North Kivu, South Kivu and Oriental provinces, Reuters said.

The news agency AFP said MONUSCO - whose acronym stands for the UN Organization Stabilization Mission in the Democratic Republic of the Congo - had begun preparations for the offensive.

UN's Kobler faces a major task to stabilize DRC Congo

The top UN envoy in Congo, Martin Kobler, who briefed the Security Council by video conference last Monday, has not yet said when the offensive will actually begin.

Ban prompts Kabila

During a phone call on Wednesday, UN chief Ban Ki-moon urged DRC Congo President Joseph Kabila to be ready to take "decisive action" against the FDLR rebels.

Will Kabila concede to UN pressure?

UN officials have said the Congolese president's support for MONUSCO has been lackluster and accuse Kabila of failing to hold senior officers to account for past human rights violations attributed to Congolese army personnel.

African regional leaders are due to discuss the intended offensive at a summit in Angola's capital Luanda next week.

Late on Friday, Tanzanian President Jakaya Kikwete said his country's troops with the UN force would help to "ensure that the eastern DRC is free of armed groups.

Kikwete dismissed a Rwandan government accusation that Tanzania favored the FDLR as "preposterous." Tanzania borders both eastern DR Congo and Rwanda.

Disarmed rebels 'once and for all'

As the UN authorized the campaign on Thursday, the US ambassador to the UN Samantha Power said the FDLR rebels must be disarmed "once and for all."

"Twenty years of genocide in Rwanda; there should be no further preconditions or delays in bringing the FDLR's long history of brutality and impunity to an end," Power said.

Eastern Congo's unrest, involving various militias, is fueled by rivalry for control of the region's vast mineral resources.

The January 2 surrender deadline imposed on the FDLR was set last July by member nations of the Southern African Development Community and the International Conference on the Great Lakes Region.

ipj/gb (AFP, Reuters, AP)