The withdrawal of the United States from the Paris Agreement in 2017 may make it hard to raise the money to fight climate change, former United Nations Secretary-General Ban Ki-Moon warned on Tuesday.

Speaking to CNBC at the Singapore International Water Week, he said: "Now with the United States pulling from this Paris agreement, I’m concerned now how to mobilize the necessary financial support for many developing countries who do not have the capacity to address this climate change issues. They do not have any responsibilities historically speaking. Therefore it is absolute necessary that the international community uses its political will to work on this matter.”

He added, "I sincerely hope that the U.S. will come back as it realizes it has a global moral political responsibility ... U.S. is the only country now who is stepping back from this global agreement.”