Washington said the agreement marked a new chapter in climate diplomacy after six years of disputes with major allies since President George W. Bush pulled out of the Kyoto Protocol, the main existing plan for combating warming.

But despite its dramatic turnaround in the meeting, which approved a "roadmap" for two years of negotiations to adopt a new treaty to succeed Kyoto beyond 2012, the White House said it still had "serious concerns" about the way forward.

"This is the defining moment for me and my mandate as secretary-general," U.N. Secretary-General Ban Ki-moon said after making a return trip to Bali to implore delegates to overcome deadlock after the talks ran a day into overtime.