Chinese Foreign Minister Wang Yi's cautionary call to Russia and Ukraine last Saturday to not let their seven-month-old war "spill over", and to pursue a fair and pragmatic diplomatic solution, could not have been more timely. It came as Russia proceeded with a referendum to cement its hold on four occupied areas of eastern and southern Ukraine, and amid fears that having suffered a series of battlefield reverses, Moscow may turn to nuclear weapons. The referendums initiated last Friday were described by United States President Joe Biden as a "sham" to annex parts of Ukraine in blatant violation of international law. Kyiv says residents were coerced into voting and could not leave the regions during the vote.

The war, Russia's gambit to halt what it saw as an effort by the US and its allies to expand Nato into its strategic backyard, has gone badly from the start for Moscow. It also galvanised the Western alliance, which sent billions of dollars worth of military equipment and weapons to Ukraine. Mr Wang's remarks on a spillover - which could be interpreted to include radioactive material from nuclear weapons being blown across borders - follows an explicit warning by Russia's former leader Dmitry Medvedev, an ally of President Vladimir Putin, that all weapons in Moscow's arsenal, including nuclear weapons, could be used to defend territories incorporated into Russia. Mr Putin has issued such threats himself. The White House warned Mr Putin that any use of nuclear weapons would have "catastrophic consequences" for Russia.