U.S. President Barack Obama and Chinese President Xi Jinping agreed after speaking over the phone that the two nations would work together on a climate change agreement.

"Both leaders agreed that the Paris conference presents a crucial opportunity to galvanize global efforts to meet the climate change challenge," the White House said in a statement, reported The Economic Times. 

Both Obama and Jinping, leaders of the largest economies and the largest polluters of the world, attended the opening ceremony of the climate meet on Nov. 30.

While a deal is still to be reached, Jinping is reported to have sought to strengthen coordination with all parties, so as to ensure that the Paris climate summit reaches an accord as scheduled.

"We still have some distance to cover before reaching our final deal, and some key issues remain unresolved. Developed countries should play the leading role and make greater efforts," said Chinese foreign ministry spokesperson Hua Chunying according to AFP.

The final draft of the text is scheduled to be presented on the morning of Dec. 12. "All the conditions are ripe for a universal and ambitious agreement. We will never find a momentum as favorable as in Paris, but now the responsibility lies with ministers, who tomorrow [Saturday] will make their choice. I will present them a text that will be the most ambitious and balanced as possible," said French foreign minister Laurent Fabius, who has been working on the draft agreement, reported The Guardian.

United Nations secretary general Ban Ki-moon was of the opinion that the talks were the most complicated and difficult negotiations he had ever been involved in. "I have been attending many difficult multilateral negotiations, but by any standard, this negotiation is most complicated, most difficult, but most important for humanity," Ki-moon said.