Fourteen people have been killed in fighting between rebels and government forces in the Ituri region of the Democratic Republic of Congo.
A local army commander said 12 militiamen and two soldiers were killed during an attack by the Ituri Patriotic Resistance Front (FRPI).
In July three rebel groups in Ituri agreed to a ceasefire ahead of the first round of presidential elections.
The second round is due to take place at the end of October.
United Nations officials had hoped the east would remain quiet ahead of the second round.
"The fighting was very serious and lasted seven hours," General Nsiona Mbuayama told Reuters news agency by phone from near Bunia.
"The militia fled in the end, taking some dead, but they left at least 12 bodies."
Some of the worst fighting during DR Congo's conflict has taken place in the north-eastern Ituri region, where local ethnic conflicts have been fuelled by clashes over minerals.
The FRPI militia, led by a man known as Cobra Matata, is one of several groups that has not joined the peace process. President Joseph Kabila and ex-rebel leader Jean-Pierre Bemba are contesting the run-off polls on 29 October.
The UN is spending $1bn a year on its 17,000-strong peacekeeping mission in DR Congo - the largest in the world.