The Democratic Republic of Congo on Thursday rejected a United Nations ultimatum for two tainted generals leading an offensive against Rwandan rebels in the country's east to be replaced.

"For us, we would only replace someone in the (army high) command if that person had been convicted by our military courts. Yet, no such thing has happened," government spokesman Lambert Mende told a press conference in Kinshasa.

The UN's 20,000-strong Monusco force had been working with Congo's army on a plan of attack against the Democratic Forces for the Liberation of Rwanda (FDLR), an ethnic Hutu militia based in eastern Congo for more than two decades.

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But in a surprise move, the army unilaterally announced last week the launch of operations, without the UN troops.

The army also announced that Generals Bruno Mandevu and Sikabwe Fall would be leading the offensive, despite being on a UN "red" list of known human rights violators.

UN officials reacted by giving Kinshasa until February 13 to sack the two generals or forfeit Monusco's support for the operation.

Shrugging off the threat Mende announced that the two generals, who had "always worked with the United Nations", would remain in charge of the offensive.

"It's a sovereign decision," Mende said, declaring that DR Congo was "not under anyone's supervision".

The FDLR was established by ethnic Hutus who fled Rwanda following the 1994 genocide of 800,000 people, mostly minority Tutsis.

Opposed to President Kagame's Tutsi-dominated government, they are accused of carrying out brutal attacks on civilians in eastern DR Congo and of smuggling gold and charcoal.

Several prominent FDLR leaders are wanted for suspected crimes against humanity.