The Democratic Republic of Congo's army has recaptured the eastern town of Bunagana, one of the last remaining strongholds of rebel group M23.
Government officials and witnesses say troops entered the town near the Ugandan border on Wednesday after M23 abandoned its positions there.
The rebel group seized Bunagana and other towns in Congo's North Kivu province when it launched a rebellion last year.
There has been heavy fighting in the region since last Friday when U.N.-backed Congolese forces launched an effort to retake the towns.
The fighting over the past few days has prompted thousands of civilians to flee across the border into Uganda. The U.N. refugee agency (UNHCR) says it expects the number of civilians seeking shelter in Uganda to swell to 10,000 by the end of Wednesday.
The agency's Uganda spokeswoman, Lucy Beck, says a first wave of civilians fled in anticipation of fighting, but the situation changed on Wednesday.
"The people who have arrived today, the biggest majority of them have come because they are in areas that are being attacked," she said. "So, many have seen the fighting. They have heard the bullets and that's why they have crossed."
Beck says relief workers are struggling to cope with the influx of refugees.
"It is a struggle. At the moment, we have in place assistance for about 5,000 people so what we are doing right now is working on ... more shelters so that we can provide a roof over people's heads and also working on the hygiene situation, providing latrines for people to use. These are the two key areas."
M23 consists of rebel fighters who joined the Congolese army in a 2009 peace deal but later defected after complaining of poor treatment.
Earlier this month, the U.N. said the peace talks in Uganda between the government and the rebels had stalled. Negotiators said the two sides remained apart over proposed amnesty for the rebels.
Some information for this report was provided by AP and AFP.