A military offensive in eastern DRC is likely to force nearly 370,000 people from their homes, the United Nations said on Thursday.
The offensive was launched last month by Congolese troops against Ugandan militants.
The fallout from a joint effort by Congo and Uganda to defeat the Allied Democratic Forces (ADF) will compound Africa's worst displacement crisis and further stretch meagre humanitarian resources.
Persistent conflict in Congo's eastern borderlands with Uganda, Rwanda and Burundi and insurrection in the centre of the country have displaced 4.3 million people internally.
Last year, it led the United Nations to declare Congo a level three humanitarian emergency - on par with Iraq, Syria and Yemen.
The campaign against the ADF is expected to displace 196,300 people in Beni territory and another 173,200 people in neighbouring Lubero territory, the UN Office for the Coordination of Humanitarian Affairs said in a report.
More than 532,000 people in the two territories near the Ugandan border fled their homes in 2016 and 2017, largely driven out by attacks by the ADF and other armed groups as well as military responses, the report said.
"The absence of protection measures for civilians in the most affected zones risks worsening. The risk of shells falling on civilian sites ... cannot be excluded," it said.
Congo's army spokesman could not be reached immediately for comment.
A spree of massacres in Beni territory since 2014, most carried out with hatchets and machetes, killed about 1,000 people. The government has blamed nearly all the attacks on the ADF, but independent experts say some Congolese soldiers have also been involved.
On Jan. 13, the Congolese army announced a general offensive against the ADF after an attack on a UN base in December blamed on the ADF that killed 15 Tanzanian peacekeepers .
The ADF has operated inside Congo since the 1990s. Congolese and UN troops have conducted repeated offensives against it, but the group always managed to bounce back. It is considered one of the most lethal of Congo's dozens of armed bands.
Separately, a local army spokesman in eastern Congo's South Kivu province said on Thursday that fighting between the military and Mai Mai Yakutumba militiamen since Jan. 20 had killed 48 rebels and seven Congolese soldiers.
Yakutumba fighters advanced to within kilometres of the lakeside city of Uvira in September before being repelled by Congolese troops with significant support from UN troops .