Barack Obama will tell the United Nations General Assembly Tuesday that the United States will "do what we must" to stop Iran from getting a nuclear weapon, according to excerpts from his planned speech.

"Make no mistake: A nuclear-armed Iran is not a challenge that can be contained. It would threaten the elimination of Israel, the security of Gulf nations, and the stability of the global economy," it adds. "It risks triggering a nuclear-arms race in the region, and the unraveling of the non-proliferation treaty. That is why a coalition of countries is holding the Iranian government accountable. And that is why the United States will do what we must to prevent Iran from obtaining a nuclear weapon."