Mr Kony is thought to have been rebuilding his forces
The Democratic Republic of Congo's army and the UN have begun a military operation to try to contain the activities of rebel leader Joseph Kony.
The campaign follows failed attempts to negotiate an end to the rebellion by his Lord's Resistance Army.
Congo's army has sent 200 troops to the northern town of Dungu, where hundreds have sought refuge from the LRA.
The LRA fought a 20-year war against the government in northern Uganda. Some two million people were displaced.
In April, Mr Kony refused to sign a deal agreed by his representatives after nearly two years of talks.
The BBC's Africa editor Martin Plaut says Mr Kony has begun strengthening his forces, using the respite he gained during the protracted negotiation process.
Mr Kony is now seen as a growing regional menace, looting villages and abducting civilians from the Central African Republic (CAR), Sudan and Congo, he says.
Between January and March he is reported to have abducted a further 300 people to act as porters, fighters and sex slaves.
He is also reported to have six new bases in northern Congo and to be running diamond mines in the CAR.
UN military spokesman Col Jean Paul Dietrich told the BBC that the new campaign aimed to deter or prevent human rights violations by the LRA against the local population.
"The operation will last until there is no more danger for the local population in the north of DRC."
Some 900 more troops are expected to reinforce the initial deployment of 200.
Joseph Kony has always managed to elude efforts to neutralise his group, our Africa editor says.
An operation involving 80 Guatemalan special forces under UN auspices in January 2006 resulted in eight of the troops losing their lives.
The LRA leader is accused of numerous war crimes, including abducting and mutilating civilians and forcing thousands of children into combat.