President Barack Obama singled out US ally Israel on Wednesday as the only country to publicly oppose the deal between world powers and Iran to curtail Tehran's nuclear program.

"So this deal is not just the best choice among alternatives, this is the strongest non-proliferation agreement ever negotiated," Obama said, in a speech to defend the accord.

"And, because this is such a strong deal, every nation in the world that has commented publicly -- with the exception of the Israeli government -- has expressed support."