About 1,300 civilians have died from conflict and violence in the Democratic Republic of Congo in just a matter of months, while over half a million people have fled their homes, the UN said Friday.
Some attacks "may amount to crimes against humanity and war crimes," United Nations rights chief Michelle Bachelet warned.
Her office said the casualty toll in the east of the vast country had soared in recent weeks as conflicts in Ituri, North Kivu and South Kivu provinces had spread, "with disastrous repercussions for the civilian population."
Armed groups, it said, had perpetrated massacres and atrocities, while government forces had also committed major breaches.
"I am appalled by the increase in brutal attacks on innocent civilians by armed groups, and by the reaction of the military and security forces who have also committed grave violations," Bachelet said in a statement.
In Ituri, rights investigators found that violence spread into new areas after the biggest armed group, CODECO, splintered following the killing of its main leader, Ngudjolo Duduko Justin, in March.
CODECO -- for the Cooperative for the Development of the Congo -- is mainly drawn from the Lendu ethnic group.
The Lendu are predominantly sedentary farmers and have historically clashed with the Hema community of traders and herders.
The UN said CODECO and other Lendu fighters had for years "pursued a strategy of slaughtering local residents" in a bid to control resources.
"So far, to their credit, the targeted communities have refrained from retaliating," Bachelet said.
The UN said violence committed by the armed groups in the region had grown "increasingly more gruesome", pointing to sexual violence, beheadings and the mutilation of corpses.
Between last October and the end of May, at least 531 civilians were killed by armed groups in Ituri, 375 of them since March, it said.
Congolese armed forces and police also allegedly killed 17 civilians during the same period, it said.
- Kivu atrocities -
In the neighbouring Kivu region, hundreds of civilians have died and hundreds of thousands have fled their homes, the Un said.
In North Kivu, military operations launched by government forces last November have led to retaliatory attacks by the main armed group, the Allied Democratic Forces (ADF), that have killed at least 514 civilians, the statement said.
The UN said the fighters had used machetes, axes and heavy weapons, and had also been abducting children, attacking schools and hospitals.
The security forces, it added, have also been responsible for killing dozens of civilians.
The surge in violence since September last year has forced more than 400,000 civilians in the region to flee their homes, rights office spokeswoman Marta Hurtado told AFP.
In South Kivu, meanwhile, a resurgence of ethnic-based violence in recent months has left at least 74 civilians dead, while dozens of women and children have been raped, the UN said.
The violence there has spurred more than 110,000 people, mainly women and children, to flee since January, Hurtado said, adding that the displacement had soared since March.
Elsewhere in the DRC, the UN detailed violence and killings in the coastal Kongo Central province and in the capital Kinshasa, where at least 62 civilians were killed in military and police operations against militants between March 30 and April 24 this year.
Bachelet called on Congolese authorities to "take all necessary measures to prevent the repetition of such grave violations."