He says the commitments made to lock down weapons-grade uranium and plutonium, and curb nuclear technology-smuggling are "at once bold and pragmatic".
And Obama is vowing to follow up on the results of the two-day conference in Washington.
Not only are there specific plans for keeping nuclear materials out of the hands of terrorists - there's a plan for a progress summit in two years.
Obama also says there must be consequences for Iran's nuclear defiance, such as meaningful sanctions.
U.S. officials say two countries that once held out against sanctions -- Russia and China -- have now agreed to talk them over.
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