The treaty, signed by President Barack Obama and Russian President Dmitry Medvedev in 2010, limits each country to no more than 1,550 nuclear warheads and 700 missiles and bombers deployed, and provides for extensive on-site inspections to verify compliance.
During the US presidential campaign, Biden stated that he was in favor of maintaining New START, which was negotiated during his tenure as Vice President under Obama.
Russia had long proposed to extend the pact without conditions or changes, but the Trump administration waited until last year to start talks and made the extension conditional on a number of demands. The talks stalled and months of negotiations failed to reduce the differences.
After both Moscow and Washington withdrew from the Intermediate-Range Nuclear Forces Treaty of 1987 in 2019, New START is the only remaining nuclear weapons control agreement between the two countries.
Earlier this month, Russia announced it would follow the US in withdrawing from the Open Skies Treaty, which allowed surveillance flights over military facilities to build trust and transparency between Russia and the West.