All sides in the conflict in the Democratic Republic of Congo are guilty of murder, rape and forcing children to fight, Human Rights Watch says.
Thousands of Congolese are fleeing to Uganda
The New York-based human rights group says the UN has been slow to react to the worsening crisis in the east which is developing into a Hutu-Tutsi war.
The Congolese army has threatened an all-out offensive against both Tutsi and Hutu militias in the region.
Refugees have been streaming across the border into Uganda in their thousands.
More than 370,000 villagers have been displaced by the fighting in the Kivus since the start of this year and an estimated 8,000 have crossed the border since the weekend.
The BBC's East Africa correspondent Karen Allen says observers fear the fighting could develop into a proxy war between Hutus and Tutsis on Congolese soil.
Dissident Gen Laurent Nkunda accuses the Congolese army of receiving backing from Rwandan Hutus - the Democratic Forces for the Liberation of Rwanda (FDLR) - who fled into DR Congo after the genocide in 1994.
The HRW report - Renewed Crisis in North Kivu - documents the ongoing rapes and murders that are blamed on all sides.
KEY FORCES IN THE KIVUS
FLNK - new group made up mainly of Congolese Mai Mai with some Rwandan Hutus formerly in the FDLR
FDLR - Hutu militia made up of former Rwandan soldiers and others who fled into Congo after the 1994 genocide
FARDC - Congolese army
Gen Laurent Nkunda, with an estimated 5,000 soldiers
Monuc - UN Mission in the DR Congo
It has accused Kinshasa of following what it calls "a confusing and contradictory" course in its dealings with the FDLR, seen as a destabilising factor in the east.
"The FDLR is supposedly committed to overthrowing the current government of Rwanda, but in recent years its members have attacked Congolese civilians more than they have engaged the Rwandan military," the report says.
United Nations peacekeepers serving in the region have been powerless to intervene in the battles between government forces and three separate militias.
The government in Kinshasa has threatened an all-out offensive against both the Mai Mai and Gen Nkunda's forces which have ignored deadlines to lay down their weapons.
The report says more must be done to assure the security of civilians in the face of threats of this major military offensive by government troops.
"UN peacekeepers must use all their military and civilian resources to ensure protection for vulnerable civilians," HRW researcher Anneke Van Woudenberg said in a statement.
"They must denounce human rights violations when they occur and be ready to respond swiftly to new threats."
Speaking to the BBC on Monday, the pro-Hutu Mai Mai militia leader Kabamba Kasereka said his men would not be disarmed before the men fighting for Gen Nkunda.
The renegade general meanwhile says his 5,000-strong militia is defending Congolese Tutsis against attacks by Hutus from the FDLR.
Members of both the Mai Mai and the FDLR have claimed to be fighting alongside the government forces.
A five-year war in DR Congo ended in 2003, but the 17,600 UN peacekeepers in the country (4,300 of them in North Kivu alone) have struggled to keep a lid on instability since then.