The army of the Democratic Republic of Congo says it has regained control of the entire eastern area of Masisi from rebels loyal to warlord Bosco "Terminator" Ntaganda.
The army has declared a ceasefire and given the rebels until Thursday to surrender.
Tens of thousands have fled their homes in the area, after weeks of fighting.
Gen Ntaganda, known as "The Terminator", is wanted for war crimes by the International Criminal Court.
The ICC accuses him of recruiting child soldiers for the same rebel group as Thomas Lubanga, who in March became the first person to be convicted of war crimes by the ICC.
His troops last month defected from the army and the Congolese authorities say they want to arrest him but put him on trial themselves, rather than sending him to The Hague.
Several hundred troops loyal to Gen Ntaganda had seized two towns in Masisi, near the North Kivu capital, Goma, but army chief Lt-Gen Didier Etumba Longila said the whole area had now been "secured".
However, army spokesman Lt Col Sylvain Ekenge admitted that a new senior army commander, Col Makenga, on Friday joined the rebellion.
Thousands of people have fled across DR Congo's borders to Rwanda and Uganda.
Gen Ntaganda was born in Rwanda, where he fought with the ethnic Tutsi rebels who brought current President Paul Kagame to power and ended the genocide in 1994.
Some Congolese army sources say Rwanda is still backing Gen Ntaganda and his rebels, who are mostly Kinyarwanda-speakers.
This was denied by President Kagame, who last week told Jeune Afrique magazine that the situation in North Kivu was purely a Congolese issue.
Rwanda has previously backed several rebel groups in DR Congo but relations have improved in recent years.
As well as Lubanga's UPC rebel group, Gen Ntaganda was also part of the CNDP militia which threatened to invade Goma in 2009, leading some 250,000 people to flee.
He and his troops were integrated into the national army later that year, before defecting in April.
People in and around the town of Goma blame them for persistent unrest - including looting and rape - since the formal end of DR Congo's war in 2003.