Chinese President Xi Jinping and his US counterpart Barack Obama have thrown their collective weight behind an "ambitious climate agreement", as marathon global talks reach a crescendo in Paris.
The leaders of the world's two biggest economies, and its two biggest polluters, discussed the crunch talks by telephone on Friday (local time), according to officials in Beijing and Washington.
The White House said both leaders agreed the negotiations presented a "crucial opportunity to galvanise global efforts to meet the climate change challenge."
"They committed that their negotiating teams in Paris would continue to work closely together and with others to realise the vision of an ambitious climate agreement," said the White House.
Xi and Obama both attended the UN summit's opening ceremony on November 30.
China's foreign ministry said that Xi had pressed for the two governments to "strengthen coordination with all parties" and "make joint efforts to ensure the Paris climate summit reaches an accord as scheduled."
Xi was said to add that a deal would be beneficial to the international community.
A deal has yet to be reached at the gathering, but sleep-starved envoys tasked with stymieing catastrophic climate change aim to wrap up a historic accord on Saturday after a second all-night session of talks.
China and the US are the world's two largest carbon emitters, though China is estimated to have released nearly twice as much as the United States and around two and a half times the European Union.
The Asian giant pledged last year to peak carbon dioxide output by "around 2030" - suggesting at least another decade of growing emissions.
"We still have some distance to cover before reaching our final deal, and some key issues remain unresolved," said foreign ministry spokesperson Hua Chunying on Friday.
"Developed countries should play the leading role and make greater efforts," she said, while calling upon all participant countries to "show their flexibility" and "narrow differences."