Thirty-five countries have pledged to turn international nuclear security guidelines into national laws, signing onto the initiative at a nuclear summit in The Hague, Netherlands.
The initiative - pushed by the Netherlands, the United States and South Korea - also requires participating nations to open their security procedures to independent review.
In addition to the three countries that promoted the initiative, Britain, France, Germany, Israel, Japan, South Korea and Turkey are among the 35 nations that signed on to it. Delegations from 53 countries are participating in the two-day Hague summit.
Miles Pomper of the California-based James Martin Center for Nonproliferation Studies said, "We need to get the rest of the summit members to sign up to it, especially Russia."
On Monday, U.S. President Barack Obama and Japanese Prime Minister Shinzo Abe announced at the Hague summit an agreement under which Japan will hand over hundreds of kilograms of weapons-grade uranium and plutonium to the United States, where it will be converted into proliferation-resistant forms.