LONDON (Reuters) -Russia told the United States on Monday that the last remaining pillar of bilateral nuclear arms control could expire in 2026 without a replacement due to what it said were U.S. efforts to inflict "strategic defeat" on Moscow in Ukraine. Both Russia and the United States still have vast arsenals of nuclear weapons which are currently partially limited by the 2011 New START Treaty, which in 2021 was extended until 2026. What comes after Feb. 4, 2026, however, is unclear, though Washington has indicated it wants to reach a follow-on agreement with Russia.