LE BOURGET, France, Safar 21, 1437, Dec 3, 2015, SPA -- U.N. Secretary-General Ban Ki-moon says he's encouraged that 150 world leaders — an "unprecedented" number — told the opening of the climate summit that they were in Paris to deliver an agreement to tackle global warming, according to AP. The U.N. chief told reporters at U.N. headquarters in New York before flying back to Paris on Thursday night that this gave strong impetus to negotiations. Now, he said, the negotiators have a lot of work to do because "key issues remain unresolved, and there is not much time left." Ban said the leadership of the U.S., the world's largest economy, "is crucially important" and he expressed appreciation for President Barack Obama's "strong leadership" and "very strong commitment." -- SPA 01:18 LOCAL TIME 22:18 GMT www.spa.gov.sa/w