Citing multiple attacks and counter-attacks between Hema herders and Lendu farmers, UNHCR spokesperson Babar Baloch told journalists in Geneva that the situation had worsened in recent days.
The development comes amid reports of intense fighting between the Congolese armed forces (FARDC) and non-state armed actors in Djugu territory, as the authorities attempt to bring the situation under control in the vast, resource-rich region.
"People are fleeing attacks and counter attacks in Djugu Territory, with reports of both communities forming self-defence groups and being involved in revenge killings", Mr. Baloch said.
"The details we are receiving from our partners, and also some of the displaced", he said, included reports of "brutalities against civilians, killings, sexual violence, and other extreme forms of violence against civilians", noting that UNHCR's warning is based on information received from sources in 125 locations.
Three of Ituri's five administrative territories - Djugu, Mahagi and Irumu - have all seen mass displacement after self-defence militia reportedly carried out "revenge killings", according to UNHCR.
In response to fears that the situation could escalate further, the UN peacekeeping mission in DRC, which goes by the French acronym MONUSCO, has set up three temporary military bases in Djugu and Mahagi.
Teams have also been deployed to assess the situation and engage with communities and the authorities to help prevent more attacks.
Simmering rivalry between the Hema and Lendu goes back decades; in the five-year war which began in 1998, thousands were killed.
Then, as now, there is concern about the humanitarian situation in Bunia, the regional capital of Ituri, amid reports from UNHCR that those trying to reach the relative safety of sites there and surrounding the urban centre "are reportedly blocked by armed youth from both ethnic groups", while others "are trying to cross Lake Albert into Uganda".
To date, the majority of those forced to flee violence have found shelter with host communities, while some 30,000 people have arrived in displacement sites where conditions were already dire, with many needing shelter and health care, UNHCR's Mr. Baloch said.
In response to a journalist's question as to whether the mass displacement risked complicating efforts to tackle the ongoing Ebola virus disease outbreak north-eastern DRC, World Health Organization (WHO) spokesperson Tarik Jasarevic said that the "mobility" of people in Ituri and neighbouring North Kivu was a "risk factor".
He added: "Every time you have people moving in high numbers, it's more complicated to work on follow-ups: contact-tracing, follow-ups on people basically who are supposed to be observed on a daily basis, or for 21 days" - the incubation period for the disease.
So far, DRC's latest Ebola outbreak has claimed 1,449 lives and infected 2168 people since it was declared on 1 August last year, said Mr. Jasarevic.