Officials in eastern Congo say heavy fighting has erupted in a rebel stronghold near the border with Uganda.

Julien Paluku, the governor of North Kivu province, confirmed the clashes near Bunagana on Wednesday.

A spokeswoman for the United Nations refugee agency in Uganda says more than 5,000 Congolese citizens already had fled across the border, and that number could soon double.

She said humanitarian workers could hear gunfire from the Bunagana border post just a few kilometers (miles) away.

Meanwhile, a Ugandan army spokesman, Lt. Ninsiima Rwemijuma, said that two militants from the M23 movement had surrendered to Ugandan border authorities Wednesday morning.

The Congolese military already has managed to seize back control of six towns in recent days from the M23 rebels.