A UN military officer in the Democratic Republic of Congo has said the response to a disarmament deadline for local militias was "not encouraging".
Half the fighters in Ituri are under 18, the UN says
Col Hussein Mahmoud, deputy commander of UN forces in the eastern Ituri region, said fewer than half of 15,000 fighters had given up their weapons.
Col Mahmoud said UN peacekeepers would now act to forcibly disarm those who flouted the midnight deadline.
He said the militias had committed an appalling catalogue of murder and rape.
Vicious ethnic warfare, fuelled by ready access to weapons, has cost the lives of tens of thousands of civilians in the province.
"We will go after them (militias), we will take them. We know their areas, we know their camps," Col Mahmoud said.
The main militia groups in Ituri signed up to the disarmament process last September.
Half the fighters in the eastern Ituri region are under 18 years old and some are as young as eight, UN officials say.
They have been caught up in ethnic violence that has left many civilians dead and many more homeless.
Some leaders have been rewarded with high-ranking posts in the new integrated Congolese army, the BBC's Ishbel Matheson in Ituri says.
But other powerful warlords have dragged their feet over the weapons surrender, our correspondent says.
She adds that they will now be waiting to see whether the UN matches its tough words with action.