The United Nations is pulling its support for a Democratic Republic of Congo military operation against rebels after Kinshasa missed a deadline to sack two generals, a UN official said Saturday.

The UN's 20,000-strong MONUSCO force had been working with Congo's army on a plan to drive out the Democratic Forces for the Liberation of Rwanda (FDLR) rebels from the east of the country.

The planned joint offensive reached an impasse when UN officials demanded that two leading generals accused of human rights violations be replaced as a condition for supporting the military action.

"The initial two-week period ... has expired," the official told AFP.

"The next step is the dispatch of formal letters to the relevant Congolese authorities concerning the cessation of support," the official said.

The correspondence will be sent by the end of the week, the official said.

DR Congo's President Joseph Kabila's government this month rejected a UN ultimatum to replace the two generals who are on a UN "red" list of known human rights violators.

UN officials told Kinshasa to fire the two generals or forfeit MONUSCO's support for the operation.

The UN move was limited to the planned operation against the FDLR and did not affect other military campaigns against the many rebel groups that roam the eastern DR Congo.

The United Nations is pushing for the disarming of dozens of rebel and splinter groups after two decades of conflict in eastern DR Congo, much of it fueled by the lucrative trade in minerals.