Developing countries are demanding a clear commitment to the financial contribution agreed during the Copenhagen summit in 2009 as part of the climate deal being negotiated in Paris.
"I have been urging the developed world leaders that this must be delivered," Ban told reporters at UN headquarters yesterday.
"This is one very important promise."
Negotiators from 195 nations are haggling in Paris over a universal accord to slash greenhouse-gas emissions but the G77 group of developing countries plus China have warned there will be no deal without financing.
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Ban said that of the USD 100 billion to be mobilized by 2020, USD 62 billion has been raised.
"Now we have another five years to go. And everybody said that it is doable, and it can be presented in a credible way," he added.
The dispute over climate financing has revolved around the sources of financing, which would be shared among governments, international institutions like the World Bank, and other private and public sources.