U.S. President Barack Obama on Thursday called the Supreme Court's decision to delay implementation of his administration's Clean Power Plan "unusual" and expressed confidence that the White House would prevail.

"We're very confident that we're on strong legal footing here," he told a group of Democratic donors in California in his first public remarks about the move.

In Washington, Gina McCarthy, Obama's head of the Environmental Protection Agency, told state energy and environmental regulators that the ruling "is not going to slow us down."