Russia and the US signed a treaty on civilian nuclear cooperation on Tuesday, the last day of Vladimir Putin's presidency.
The two-decade old agreement for cooperation in developing reactors, storing and shipping uranium and nuclear materials was a key element of talks between Putin and US President George W Bush at the 2006 Group of Eight summit in St Petersburg.
Sergei Kiriyenko, the head of state-owned nuclear power firm Rosatom, and US Ambassador William Burns signed the document in Moscow.
The White House said Bush was "pleased" with the agreement, which would set the groundwork for expanded cooperation in nuclear energy and the sale of civil nuclear commodities to Russia by US companies.
"The conclusion of this agreement, which advances US-Russia non-proliferation and civil nuclear energy cooperation goals, has been a priority for both President Bush and President Putin," White House spokeswoman Dana Perino said in a statement.
The US Congress must still approve the agreement.
Burns will leave his post Wednesday, when president-elect Dmitry Medvedev takes office. He has been promoted to the number three spot in the US State Department, where he will be in charge of the country's strategy on Iran.
Russia's expertise in nuclear energy has turned it a great profit since the end of the Soviet Union, but Moscow's aid in building Tehran's first nuclear reactor at Bushehr has scandalised US politicians who sees Iran's nuclear programme as a cover for ambitions to build weapons.