UN investigators have uncovered mass human rights abuses in Congo in the 1990s including the possible genocide of Hutu refugees by Rwandan forces, a French newspaper reported Thursday.

A leaked report by the United Nations High Commissioner on Human Rights (UNHCR), details murders, rapes and looting by fighters from various countries in two wars that rocked the former Zaire between 1993 and 2003, Le Monde said.

The most serious claims target Rwanda, whose forces along with Congolese troops allegedly shot, clubbed and axed to death vast numbers of ethnic Hutu refugees in Congo, including women, children and the elderly in the late 1990s.

The total number of victims of war crimes by forces from various countries operating in the country, known since 1997 as the Democratic Republic of Congo, is "probably several tens of thousands," the UNHCR report said, according to the newspaper.

After the genocide of Tutsis in Rwanda in 1994, about a million Hutus fearing reprisals fled across the western border to Congo, where they were later targeted by Rwandan Tutsi forces.

Le Monde quoted the UNHCR report as saying that "the systematic and generalised attacks (against Hutus in Congo) have several damning aspects which, if proved by a competent court, could qualify as crimes of genocide."

The allegations were among some of "the most serious violations of human rights and international law" in Congo according to the report, which accuses forces from several other neighbouring countries of crimes over the 10 years.

Citing unnamed sources, Le Monde said Rwandan President Paul Kagame had fought to cover up the report, threatening to withdraw Rwandan troops from UN peacekeeping missions.

The daily cited unnamed Rwandan sources dismissing the allegations as "absurd".

The UN report is due to be published in September, the newspaper said.