Donald Trump has confirmed he will withdraw the US from the Paris climate change agreement.
Mr Trump said the Paris agreement disadvantaged the United States, and that he hoped to seek "a better deal".
"We're getting out," he said.
"The United States will withdraw from the Paris climate accord but begin negotiations to re-enter either the Paris accord or an entirely new transaction, on terms that are fair to the United States, its businesses, its workers, its people, its taxpayers."
The United States will cease implementation of non-binding elements of the accord "as of today".
The Paris deal "hamstrings the United States while empowering some of the world's top polluting countries" and any new agreement would need the burdens and responsibilities equally shared by nations around the world, he said.
Obama statement. pic.twitter.com/YGUYTEjo66— Simon Marks (@SimonMarksFSN) June 1, 2017
The 2015 accord united most of the world in a single agreement to mitigate climate change for the first time. It was signed by 195 countries out of 197 in a UN group on climate change, with Syria and Nicaragua abstaining.
US allies voiced dismay over Mr Trump's move, and France, Germany and Italy dismissed his suggestion that the global pact could be revised.
French president Emmanuel Macron categorically ruled out any renegotiation and said Mr Trump's decision would harm American interests and citizens.
"I tell you firmly tonight: We will not renegotiate a less ambitious accord. There is no way," he said in a televised address. "Don't be mistaken on climate; there is no plan B because there is no planet B."
Mr Trump said the United States would cease payments to the UN Green Climate Fund, in which rich countries committed billions of dollars to help developing countries deal with floods, droughts and other impacts from climate change.
The United Nations described the withdrawal as a major disappointment for global efforts to reduce greenhouse gas emissions and promote global security.
UN secretary-general Antonio Guterres, who had made last-minute plea to the United States to remain committed to the pact, was confident that "cities, states and businesses within the United States" would continue demonstrate leadership on working for "low-carbon, resilient economic growth".
Chinese and EU leaders were set to agree a joint statement backing the Paris agreement, saying it is "an imperative more important than ever".
The draft statement says rising temperatures affect national security and increase "social and political fragility", while the transition to clean energy creates jobs and economic growth, the BBC reported, before Mr Trump's announcement.
Chinese Premier Li Keqiang has said his country will honour its commitments on climate change.
Speaking on a visit to Germany, he said fighting climate change was in China's own interests.
China overtook the US as the world's biggest emitter of greenhouse gases in 2007.
Russia also said it would stick to its climate commitments, but said the Paris agreement would be affected by a US pullout.
"It goes without saying that the effectiveness of this convention is likely to be reduced without its key participants," a Kremlin spokesman said.
Mr Trump's refusal to commit to the Paris agreement caused frustration at a G7 meeting last week, with German Chancellor Angela Merkel describing the discussion as "difficult, not to say dissatisfying".