By Mark Dummett BBC correspondent in Kinshasa

A rebel movement controlling about a third of the Democratic Republic of Congo has declared that it no longer has any confidence in the head of the United Nations peacekeeping operation in the country.

The Congolese Rally for Democracy, which is backed by Rwanda, says a leaked document reveals that UN mission head Amos Namanga Ngongi is biased in favour of the government in Kinshasa.

The claims follow reports of a mutiny by dissident soldiers in the rebel-held city of Kisangani on 14 May, and reprisals in which more than 200 people are said to have to have been killed by Rwandan and rebel soldiers.

Many of the victims were unarmed civilians - the rest were soldiers and policemen whose decapitated and disembowelled bodies have been found floating in nearby rivers.

The UN has no mandate to intervene in the conflict in Congo, but it does have a mandate to protect civilians and report on what is going on.

'Human rights abuses'

Last week the UN mission accused the rebel movement, the Congolese Rally for Democracy (RCD), of grave violations of human rights.

It said it considered the reprisals unjustifiable and unacceptable.

The RCD has responded by accusing Mr Ngongi of being biased and pro-Kinshasa - referring to the capital city which is held by the government.

The RCD leader, Adolphe Onusumba, said he had been leaked a confidential UN document which proved his claim and denied that such brutal reprisals had taken place.

Mr Onusumba said he had written a letter to UN Secretary General Kofi Annan asking for a replacement for Mr Ngongi to be found.

If this was not enough for the UN peacekeeping operation, protests have been held for the past two days outside Mr Ngongi's headquarters in Kinshasa.

Hundreds of people have demanded to know why the UN stood by in Kisangani when civilians were being killed.

In Kisangani, too, residents have dubbed the peacekeepers "the observers of Congolese corpses".

Mr Ngongi has rejected claims that on the one hand he is partial and on the other that he did nothing to stop the killing.