Goma - Some 200 000 Congolese migrants have been expelled from Angola and returned home to the troubled Kasai province - an influx that could result in a humanitarian crisis.
The UN refugee agency UNHCR "is appealing to the governments of Angola and the DRC to work together to ensure a safe and orderly population movement," the body said in a statement on Tuesday.
The mass expulsions started about two weeks ago, when the Angolan government ordered the migrants - who were working in the informal mining sector in the north-east of the country - to go back to neighbouring Congo, the UNHCR said.
There have been reports of violent clashes in some parts of Angola as police tried to enforce the order, as well as reports of sexual violence and theft at border points, the body said.
"The Congolese are returning to a desperate situation, looking for safety and aid. With more arriving every day, thousands are reported to be stuck at and near the border," the statement said.
"In addition, many are likely to face difficulties due to destruction caused by recent conflict in the area," it added.
Congolese government spokesman Lambert Mende told dpa Tuesday that a team has been deployed to help those Congolese who have arrived home.
Mende said the government was also investigating "extremely serious allegations" that some of their nationals were violently expelled.