A UN spokesman said in Kinshasa on Thursday that a government soldier and seven militiamen were killed when hundreds of Nepalese UN peacekeepers and 1500 Congolese soldiers, backed up by helicopter gunships, clashed with militiamen near Fataki, about 75km north of Bunia, in Ituri province.
Another UN official said nine Congolese troops were killed in separate fighting on Wednesday with another ethnic militia near Boga, 80km southwest of Bunia.
The clashes highlighted insecurity in the east, days after millions voted in Congo's first free national poll in 40 years.
UN military operations across the country ceased in the run-up to the poll to allow as many people as possible to vote.
Latest results released on Thursday showed that with nearly 60% of polling stations counted, the "yes" vote had just over 80% - which appeared to guarantee the adoption of a constitution paving the way for elections next year.
Major Hans-Jakob Reichen, a military spokesman for the UN peacekeeping force, said: "There is a major operation going on at the moment; 375 of our men and 1500 Congolese soldiers are carrying out an operation to restore the rule of law.
"Clashes are taking place and the UN is giving fire support. So far one Congolese soldier has died and seven militiamen have been killed."
He said the militiamen were Lendu fighters who refused to join a UN-backed disarmament process and are accused of atrocities against civilians.
A UN force is trying to restore
peace after a five-year war
Near Boga, another local ethnic militia fought a bloody battle with government troops, a UN official said.
"There was fighting between the Congolese army and other militia fighters near Boga yesterday. Nine government soldiers were killed and another 30 are injured, three of them seriously," the official said.
"We are told about 30 militiamen were killed."
The world's biggest UN peacekeeping force is trying to restore peace to the Democratic Republic of Congo after the five-year war, which is estimated to have killed nearly four million people, mainly through hunger and disease.
The war officially ended in 2003, but bands of armed men still terrorise civilians in large areas of the country, particularly eastern areas where mineral riches are believed to have fuelled a conflict that at one point drew in six foreign armies.
Often accused of failing to protect civilians in Congo's eastern Ituri province, this year the UN force has carried out more robust operations with a new Congolese army drawn from the ranks of former rebel movements and existing government forces.
About 15,000 fighters signed up to the disarmament process in Ituri but several thousand are believed to have remained in the bush, persecuting civilians and resisting efforts to re-establish central government authority.
About 15,000 fighters have so far
joined the disarmament process
The UN Security Council stepped up a drive on Wednesday to rid eastern Congo of Rwandan Hutu rebels who have hidden out in the area for more than a decade and terrorised civilians.
It authorised UN sanctions to be imposed on the leaders of armed groups in Congo who have failed to fulfil promises to disarm and leave the country or prevented others from doing so.
Hutu rebels fled to Congo after helping to carry out the 1994 Rwandan genocide in which 800,000 minority Tutsis and politically moderate Hutus were killed.