Russia and the United States have agreed to reopen talks on cutting stockpiles of nuclear weapons.
US President Barack Obama and Russian leader Dmitry Medvedev on Wednesday agreed in a joint statement to launch negotiations on a replacement for the START treaty.
The Cold War-era Strategic Arms Reduction Treaty signed between the Soviet Union and the United States expires in December 2009, and Moscow and Washington have been seeking to thrash out terms of a new accord.
The 1991 treaty limits the number of missiles and warheads that each side may have.
Mr Medvedev and Mr Obama, who met in London ahead of Thursday's G20 summit, also said that they had agreed on the long-term goal of a "nuclear free" world.
The leaders' statement said the two countries intend to conclude an agreement before the Treaty expires in December.