Dr Margaret Chan said the agency would review how the whole world, and the WHO in particular, managed the outbreak "and there will be time for sharing information in a transparent and accountable manner."
"But at this point in time, it is important for us to focus our entire energy and attention to help countries who are being affected to get the job done," she said.
The head of the WHO regional office for Africa is being replaced.
During her speech to the UN conference, Chan said medical epidemics like Ebola can have wide reverberations around the globe, including on nutrition.
She criticized bans on bush meat that were imposed in some parts of Africa in a bid to contain the outbreak, after studies linked wild animals to the start of Ebola. She noted that bush meat is a principal source of food and income for people in the region.