"Russia initiated the process, and serious work has been ongoing to develop new approaches in this sphere, so far on the level of experts," said Sergei Khudoklinov, head of the National Center for Nuclear Threat Reduction.
He said Russia and the United States still disagreed on a number of points, but that "there is still time, and with political will, many problems could be resolved."
Russian Foreign Minister Sergei Lavrov said in November that a treaty to replace START-I must set lower ceilings for nuclear arsenals and limit the development of new nuclear weapons.
The START-I treaty was signed by the United States and the Soviet Union on July 31, 1991, five months before the U.S.S.R. collapsed, and remains in force between the U.S., Russia, and three other ex-Soviet states.
The three former Soviet republics, Belarus, Kazakhstan and Ukraine, have since disposed of all their nuclear weapons or transferred them to Russia, and the U.S. and Russia have reduced the number of delivery vehicles to 1,600, with no more than 6,000 warheads. The current treaty is set to expire on December 5, 2009.
The START-I treaty was followed by START-II, which banned the use of multiple re-entry vehicles (MIRV) but never entered into force and was later bypassed by the Treaty on Strategic Offensive Reductions (SORT), signed on May 24, 2002 by presidents Vladimir Putin and George W. Bush in Moscow.
SORT, which expires on December 31, 2012, limited both countries' nuclear arsenals to 1,700-2,200 warheads each. The treaty has been largely criticized for its lack of verification provisions and for not explicitly prohibiting the re-deployment of stored warheads.
Russia and the United States have already called on all countries to join the bilateral Intermediate-Range Nuclear Forces Treaty, which banned nuclear and conventional ground-launched ballistic and cruise missiles with ranges of 500 to 5,500 kilometers (300 to 3,400 miles).