A joint force of U.N. and Congolese troops has attacked Ugandan rebels in the eastern Democratic Republic of Congo.

U.N. sources say the attacks in North Kivu province Sunday were against the Allied Democratic Forces, a Ugandan rebel group that maintains bases in the DRC.

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

The troops hope to assert government control in areas dominated for years by foreign-backed rebels or local militias.

The U.N. peacekeeping mission in Congo says U.N. and Congolese troops captured the town of Nioka from ethnic Lendu rebels on Saturday.

Partial returns from last week's vote show DRC voters approving the new constitution 83 to 17 percent. The charter is designed to pave the way for national elections and help end decades of chaos and war.