Russia and the United States will sign a deal tomorrow on reducing stocks of weapons-grade plutonium, the Russian Foreign Ministry said.
Under the agreement, each country is to dispose of 34 metric tons of weapons-grade plutonium removed from military programmes by burning it in reactors, US officials said.
The United States and Russia initially reached a similar deal on plutonium disposal in 2000 but it never went into force.
The planned signing during a global nuclear security summit comes after Russian president Dmitry Medvedev and US president Barack Obama signed the "New START" treaty committing the Cold War foes to reducing their deployed nuclear arsenals.
"Tomorrow in Washington a bilateral protocol will be signed to the agreement on the disposal of surplus weapons-grade plutonium," Deputy Foreign Minister Sergei Ryabkov said in an interview broadcast on Ekho Moskvy radio station today.
Senior Obama advisor Gary Samore said on Friday the deal "is very significant in the sense that over a period of a decade or so it will remove very large quantities of weapons-useable materials, and also it's an agreement that's been long stalled.
"It was really President Obama's focus on this issue and the reset of his relationship with Russia that has finally been able to finalize this agreement."
The US-Russia Plutonium Disposition agreement would be signed by US secretary of state Hillary Clinton and Russian foreign minister Sergei Lavrov, Samore said.
The deal will provide for the United States to spend up to $400 million to transform the Russian plutonium involved, said Matthew Bunn, a nuclear expert at Harvard University.
The process would involve taking plutonium that is "ready to be put right into a weapon" and "putting it in a much more secure form for decades to come," Mr Bunn said.
He said US critics question the deal because reactors used for the Russian plutonium could potentially be remodified to produce new weapons-grade plutonium.
Mr Medvedev is due in Washington today for a two-day nuclear security summit that Mr Obama is hosting as part of his push to reduce threats from nuclear weapons and materials.