Cann said the gains from reducing nuclear material will likely trail off in the future. In absence of a global treaty on nuclear security, the next phase in improving security will be for groups of like-minded countries to lead the way.
That will put peer pressure among nations, she said, with none wanting to be seen as the most lax at safeguarding their nuclear material.
Agreeing to external checks, conducted under the auspices of the International Atomic Energy Agency, is especially important, she added.
A final summit is scheduled for 2016 in the United States, but the process of securing nuclear material will not end there.
"Obama is thinking about a sustainable nuclear security system post-2016 so creating the architecture will be his homework," said Chang-Hoon Shin, a research fellow at the Asan Institute for Policy Studies. "Sustainable, global nuclear security architecture is a long-term aim."
Associated Press writers Toby Sterling and Juergen Baetz contributed.
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