WASHINGTON — World leaders vowed Friday to confront climate change in a new international coalition that no longer includes the United States government, moving quickly to reshape global environmental alliances after President Trump’s decision to abandon the Paris climate accord.

At the White House, Scott Pruitt, the administrator of the Environmental Protection Agency, declared that the president had “nothing to be apologetic about” after announcing his decision on Thursday. He hailed Mr. Trump’s actions to “put America’s interests first” and said that “exiting Paris does not mean disengagement.”

But in foreign capitals, and in communities across the United States that vowed to continue their efforts to combat the effects of climate change, that is exactly what Mr. Trump’s withdrawal seemed to mean. International officials set in motion plans to leave the American government behind while they look for ways to stave off the direst consequences of the warming of the planet.

In Germany, Chancellor Angela Merkel said Mr. Trump’s actions “will not deter all of us who feel obliged to protect this earth.” Koichi Yamamoto, the Japanese environment minister, told reporters that Mr. Trump had “turned his back on the wisdom of human beings.” Donald Tusk, the president of the European Council, said the fight against climate change “will continue with or without the United States.”