ROME, June 1 (Reuters) - Italy, France and Germany said on Thursday they regretted U.S. President Donald Trump’s decision to withdraw from the Paris climate accord and dismissed his suggestion that the global pact could be revised.

“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,” the leaders of the three countries said in a joint statement.

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.