There has been widespread international condemnation of President Trump's announcement that the US is withdrawing from the 2015 Paris climate agreement.
UN chief Antonio Guterres's spokesman called it "a major disappointment" while the European Union said it was "a sad day for the world".
However, senior Republicans and the US coal industry backed the move.
Mr Trump said the accord "punished" the US and would cost millions of American jobs.
In an address at the White House, he said he was prepared to negotiate a new agreement or re-enter the accord on improved terms.
"I was elected to represent the citizens of Pittsburgh, not Paris," he said.
The Paris agreement commits the US and 187 other countries to keeping rising global temperatures "well below" 2C above pre-industrial levels and "endeavour to limit" them even more, to 1.5C.
Only Syria and Nicaragua did not sign up to the deal.
Why did Trump pull out of the accord?
Mr Trump characterised the Paris agreement as a deal that aimed to hobble, disadvantage and impoverish the US.
He claimed the agreement would cost the US $3tn (£2.3tn) in lost GDP and 6.5 million jobs - while rival economies like China and India were treated more favourably.

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