The United Nations reports heavy fighting between Ugandan rebels and a joint U.N.-Congolese force in the eastern Democratic Republic of Congo.

The U.N. mission in Congo says 35 Ugandan rebels have been killed, along with three Congolese government troops and an Indian U.N. peacekeeping soldier.

The U.N.-Congolese force attacked the rebels Saturday south of Beni in North Kivu province.

U.N. officials say the offensive was launched after the rebels, known as the Allied Democratic Forces, rejected repeated attempts to negotiate their return to Uganda.

This is the second U.N.-Congolese offensive against militias in the region since last week's constitutional referendum.

The troops hope to assert government control in areas dominated by foreign-backed rebels or local militias. U.N. and Congolese troops captured the town of Nioka from ethnic Lendu rebels on Saturday.