Democratic Republic of Congo rebel leader Laurent Nkunda has described as exaggerated a government claim that some 1,000 of his men had defected.
Gen Nkunda told the BBC most of the rebel fighters who surrendered did so after his talks with the government.
Correspondents speak of a worsening humanitarian crisis following weeks of clashes in the eastern Kivu region.
Medical staff in Kichanga, Gen Nkunda's stronghold, say the authorities are blocking medical supplies.
President Joseph Kabila has demanded that Gen Nkunda reintegrate all his forces into the national army.
Gen Nkunda ignored Monday's deadline to begin disarming his troops. The deadline has since been extended to an unspecified date, and government troops have advanced on Kichanga in the past week.
At the hospital in Kichanga, a doctor and 12 nurses are working in appalling conditions as they treat about 150 patients, some with gunshot wounds, and some malnourished children, the BBC's Karen Allen reports from the town.
The hospital staff told our correspondent the authorities in the provincial capital, Goma, were preventing medical supplies getting through and accusing the hospital of harbouring rebels.
The UN estimates 6,000 Rwandan Hutu rebels – known as the Democratic Forces for the Liberation of Rwanda (FDLR) – are operating in the east.
Gen Nkunda has previously accused the Congolese army of working with other local militia and the FDLR to attack him – an accusation the government denies.
On Wednesday, the government announced a plan to begin disarming the Hutu rebels.
More than 370,000 people have been displaced by the fighting in eastern DR Congo since the start of the year in a growing humanitarian crisis.