Nuclear treaty extension rejected

The United States and Russia have rejected each other’s proposals for potentially salvaging the last remaining legal constraint on their strategic nuclear forces.

Russian President Vladimir Putin yesterday called for an unconditional extension of the soon- to- expire New START treaty, but the White House called this a ‘‘non-starter’’.

Adding an edginess to the diplomatic clash, US President Donald Trump’s national security adviser, Robert O’Brien, suggested that the Russians rethink their stance ‘‘ before a costly arms race ensues’’. Trump administration officials have previously alluded to building up the US’s nuclear forces if the treaty is abandoned.

In the closing days of his reelection bid, Trump has looked for ways to boost his foreign policy record. Although he says he favours nuclear arms control, he has called New START flawed and unfavourable to the US.

Last year he withdrew the US from a separate nuclear arms treaty with Russia, and he waited until this year to begin engaging the Russians on the future of the New START deal.

The Trump administration recently proposed a one-year extension of the 2010 treaty, which is set to expire in February 2021, but said this must be coupled with the imposition of a broader cap on US and Russian nuclear warheads. Putin said yesterday a one-year extension was acceptable but should not be conditional on a wider cap on warheads.

The Trump administration’s talk of a cap, or freeze, on all categories of warheads has puzzled some US analysts, partly because the number of warheads has held steady over the past decade.

The arms control effort is hampered in part by deteriorating trust between Washington and Moscow.

The US accuses Russia of cheating and aspiring to a nuclear buildup. The Defence Intelligence Agency last year projected that Russia’s stockpile of nuclear weapons would ‘‘grow significantly’’ over the next decade, driven by an increase in shorter- range, or non- strategic, weapons that are not governed by the New START treaty.

Moscow is suspicious of US missile defences, which it believes could undermine the credibility of its strategic missiles.