World leaders have said they regret US President Donald Trump's decision to withdraw from the Paris climate accord.
Italian, German and French leaders also dismissed Mr Trump’s suggestion that the global pact could be revised.
Mr Trump had said the US would begin negotiations to re-enter either the Paris accord or "a new transaction on terms that are fair to the United States, its businesses, its workers, its people, its taxpayers."
In response, the three leaders said: "We deem the momentum generated in Paris in December 2015 irreversible and we firmly believe that the Paris Agreement cannot be renegotiated, since it is a vital instrument for our planet, societies and economies."
Italian Prime Minister Paolo Gentiloni, German Chancellor Angela Merkel and French President Emmanuel Macron urged all their allies to speed up efforts to combat climate change and said they would do more to help developing countries adapt.
Mr Macron also told Mr Trump that while France would continue to work with the US, it would no longer discuss climate issues with them, a French source said.
The US now joins Nicaragua and Syria as the only nations not subject to the pact, with Mr Trump saying his decision was based on "draconian" financial and economic burdens.
Minister for the Environment Denis Naughten described the decision as a "major setback for the international community."
He added that "it is essential that the decision of the United States does not weaken global resolve."
Former president Mary Robinson said "it is unconscionable that one of the world's largest greenhouse gas emitters would simply walk away from its responsibility ... in the interest of short term fossil fuel profits."
A spokesperson for the United Nations called the decision to leave the deal a "major disappointment."
Mr Trump's predecessor, Barack Obama, said that the Trump administration rejects the future in pulling out of the pact.
"Even in the absence of American leadership; even as this administration joins a small handful of nations that reject the future; I'm confident that our states, cities, and businesses will step up and do even more to lead the way, and help protect for future generations the one planet we've got," Mr Obama said in a statement.
European Commission President Jean-Claude Juncker called Mr Trump's decision "seriously wrong", while the commissioner for climate action and energy, Miguel Arias Canete, said "the world can continue to count on Europe for global leadership in the fight against climate change."
British Prime Minister Theresa May came under fire from political rivals for failing to join her European colleagues in signing the joint statement .
However, a subsequent statement from Downing Street said the Conservative leader told Mr Trump of her "disappointment" at the decision and stressed Britain's commitment to the pact.
Mrs May, along with the French, German and Canadian leaders, spoke to Mr Trump in separate phone calls following his announcement.
