"We agreed to pursue new and verifiable reductions in our strategic offensive arsenals in a step-by-step process, beginning by replacing the Strategic Arms Reduction Treaty [START] with a new, legally binding treaty," Russian President Dmitry Medvedev and U.S. President Barack Obama said in a joint statement after a meeting in London.
"We are instructing our negotiators to start talks immediately on this new treaty and to report on results achieved in working out the new agreement by July," the statement said.
The START-1 treaty, signed in 1991, obliged Washington and Moscow to cut nuclear warheads to 6,000 and their delivery vehicles to 1,600 by each side. The treaty expires December 5.
In 2002, an additional agreement on strategic offensive reductions was concluded in Moscow. The agreement, known as the Moscow Treaty, envisioned cuts to 1,700-2,200 warheads by December 2012. However, that treaty is largely thought to be less effective than the START treaty.
The presidents agreed that the new arms reduction treaty should cut the arms to levels lower than those envisioned in the Moscow Treaty.
Russia and the United States possess 90% of the world's nuclear weapons.
Moscow, which proposed a new arms reduction agreement with Washington in 2005, expects the United States to agree on a deal that would restrict not only the numbers of nuclear warheads but also place limits on all existing kinds of delivery vehicles.
Moscow also insists on the effective use of control mechanisms and procedures, "which the previous administration ignored categorically," according to Foreign Minister Sergei Lavrov.
