TOKYO -- Rich donor nations should offer more financial aid for Russia to dismantle its Soviet-era nuclear and chemical weapons stockpiles and help other countries keep nuclear material from terrorists, experts said at an international conference Tuesday.

Weapons specialists from governments and think tanks around the world gathered in Tokyo to assess progress in eliminating weapons of mass destruction and protecting stored nuclear waste since 2002, when the Group of Eight industrialized nations promised at least $20 billion over 10 years for the effort.

But former U.S. Senator Sam Nunn, co-chairman of the Nuclear Threat Initiative, a charity that co-sponsored the conference, said the pledges so far of $17 billion fall short of that goal -- and stressed that only a fraction of that amount had actually been spent. He urged delegates to consider the risks of inaction.

Destroying Russia's biological and chemical arms stockpiles could cost $8 billion, said Alexander Pikayev, director of Russia's Institute of World Economy and International Relations.

Other delegates said converting the plutonium of Russian nuclear warheads into less-potent spent fuel would cost additional billions of dollars and could take more than a decade.

"If you want to prevent these materials from getting into the hands of terrorists, you have to deal with the problem where it exists, and it exists in Russia," said Robert Einhorn, a security expert at the Center for Strategic and International Studies, which organized the conference.

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