"They've been fighting over fishing ponds. We know that there were clashes. There was fighting with machetes and with hunting rifles, but at present we don't know how many dead there are," Lambert Mende, DR Congo's information minister, said.

"The policemen were sent to re-establish order. I don't know why they would have been attacked," Mende said.

The violence is not linked to fighting in the DR Congo's east, in which Rwandan Hutu groups, who fled Rwanda after helping orchestrate the genocide in the 1990s, are accused of atrocities.

Joseph Kabila, the DR Congo's president, said his forces are succeeding against Rwandan militias there.

'Gaining ground'

Speaking to reporters on Friday during a visit to South Africa, Kabila said the operation against the Rwandan Hutus would continue until he "controls the whole territory".

Kabila said the situation was starting to stabilise, nine months after the offensive began, and that civilians in the province of North Kivu have begun to return to their villages.

Hundreds of thousands had been displaced as a result of the fighting.

Kabila also said troops were "gaining ground" against Ugandan fighters in the country's vast, troubled north.

Ugandan and DRC forces began a co-ordinated operation against the Lord's Resistance Army (LRA) who spread into DR Congo territory in late 2008.

The LRA, engaged in one of Africa's longest-running conflicts against the Ugandan government, has also extended its reach into Sudan and the Central African Republic (CAR).