"We know that many elements need to be explained in the future," said the UN health agency's spokeswoman Fadela Chaib.
"We believe in the virtue of transparency and accountability. WHO will do that, but in the future. Now our focus is on the response," she told reporters in Geneva.
Critics have questioned why WHO only declared an international health emergency in August, eight months after the epidemic began in Guinea.
The tropical disease, which is proving fatal in 70 percent of cases, has claimed more than 4,500 lives in West Africa, making it the largest Ebola epidemic in history.
Liberia, Sierra Leone and Guinea have been hit hardest, accounting for the overwhelming majority of the 9,200 cases registered in seven countries.
Experts warn that the infection rate could reach 10,000 a week by early December.
Even the current scale of the epidemic is unclear, due to massive difficulties gathering figures.
"We know that for the three countries, they are under-reporting," said Chaib.
"Is it ten percent, is it 20 percent? I don't know," she said.
"What we know is that we are not finding all the cases."
Medical charity Doctors Without Borders (MSF), at the forefront of the fight against the disease, had back in April said it was out of control.
'Frustrated and angry'
"We are frustrated and angry that the global response to this outbreak has been so slow and inadequate. For months, we have been pleading for more help and watching the situation deteriorate," MSF told AFP on Tuesday.
"When the outbreak is under control, it is important for every organisation to look back on their respective response and identify possible shortcomings or failures so that lessons learnt can be used in future interventions.
"We at MSF will also look at our own operations and what we could have done and said differently," the charity said.
"We must also reflect on how national and global health systems can have failed quite so badly."
For now, however, the top priority must be the immediate deployment of desperately needed assets and expertise to West Africa in order to curb the epidemic, MSF said.
There have been claims that WHO was hobbled by internal bureaucracy and turf wars — and asleep at the wheel despite extensive media coverage of the emerging crisis.
Leaks of a hard-hitting internal report have trickled into the media, but WHO insists they are from a first draft setting out the chronology of the outbreak for a future review, and have not been fact-checked or assessed by staff involved in battling the epidemic.
"We will have time to do an audit of the WHO and international response to the Ebola epidemic. Now our focus is to respond to it, try to minimize its effects on the population in West Africa," said Chaib.
The review's remit has not been set out yet, she said.
It was unclear whether WHO would hold an external audit, as it did after the 2009 H1N1 swine flu crisis.