Russia has told the United States that it will not extend the Nunn-Lugar weapons reduction and security agreement after it expires at the end of May, saying it no longer needs to receive foreign aid and is concerned about leaks of nuclear security information.

The 21-year-old cooperative program was designed to help secure the nuclear and chemical weapons arsenal of the Soviet Union after the bloc’s collapse. At a cost of about $500 million a year, it has ensured the shipment of nuclear weapons out of Ukraine, Kazakhstan and Belarus, deactivated more than 7,600 nuclear warheads, destroyed 902 intercontinental ballistic missiles and 33 submarines and secured 24 nuclear weapons storage sites.

Russia has become increasingly uncomfortable in the role of a nation that receives outside assistance, and conservatives in the United States have pointed out that the program frees up Russian money that can be spent on new armaments.

The Foreign Ministry indicated that Russia is not abandoning efforts to secure weapons of mass destruction, saying in a statement issued Wednesday evening that the country wants to create a new framework for nuclear security.

“We have received an offer from the American side for the next renewal of the 1992 agreement,” the statement said. “Our American partners know that their proposal is not consistent with our ideas about what forms and on what basis further cooperation should be built. To this end, in particular, we need another, more modern legal framework.”

The move comes just a few weeks after Russia announced it was expelling the U.S. Agency for International Development, the American foreign-aid program. Earlier this week, UNICEF also announced that it will wind up its operations in Russia by the end of the year. On Wednesday evening, Interfax quoted Deputy Foreign Minister Sergei Ryabkov as saying there was no connection between the shutdown of the aid programs and the end of the weapons agreement.

But the Kremlin has been hewing to a distinctly anti-American tone as it attempts to portray its domestic opponents as agents of the United States. At the same time, Republican presidential nominee Mitt Romney has called Russia America’s “No. 1 geopolitical foe.”

Sen. Richard G. Lugar (R-Ind.), one of two sponsors of the 1991 bill that created what is formally called the Cooperative Threat Reduction Program, was defeated by a conservative Republican in this year’s Indiana Senate primary, thus removing its principal advocate from office.

His co-sponsor, former senator Sam Nunn (D-Ga.), issued a statement Wednesday noting how much had been accomplished under the pact and adding: “I hope and expect that the U.S.-Russian partnership will be strengthened by any changes to the program.”

The Nunn-Lugar program also targets chemical weapons and has established monitoring facilities for the detection of biological weapons. Russia says it has no biological arms.

In the past decade, the program was expanded beyond the former Soviet Union and was put to use in aiding Albania to destroy its stockpile of chemical weapons.