He said withdrawal was possible out of respect for the calls from regional leaders.
Runiga said that the rebels wanted to sit down and discuss the March 23 agreement with civil society, the government and a broad spectrum of the Congolese people to come up with lasting solutions on good governance, democracy, the economy and security.
Runiga said the M23 would maintain a humanitarian corridor, and he called on people to respect the role of MONUSCO, the U.N. peacekeeping force in the region mandated to protect civilians.
MONUSCO forces took a back seat as army forces battled the rebels for control of the city last week.
Col. Olivier Hamuli, a Congolese army spokesman, said the armed forces were awaiting guidance from the government and would abide by a cease-fire until they were told to do otherwise.
The United Nations has called on the rebels to lay down their arms and withdraw immediately from Goma.
The United Nations High Commissioner for Refugees said Tuesday that aid groups had been able to resume deliveries to sites around Goma over the weekend, after fighting caused days of disruption. The U.N. refugee agency said it was trying to reach 110,000 people with supplies of food, soap and water containers.
Many of those who have fled to refugee camps around Goma are in urgent need of shelter and clean water, the UNHCR said.
"Sanitary conditions remain a major challenge due to the lack of toilets and water supply points," it said. Cases of vomiting, diarrhea and respiratory infections have already been recorded, it said, with the last due to people having to sleep outside without shelter from the rain.
The Democratic Republic of the Congo has seen far more than its share of violence over the decades. Civil wars -- most recently in the 1990s through 2003 -- have left millions dead across the country and displaced entire generations.