The United States warned on Sunday of “catastrophic consequences” if Moscow were to use nuclear weapons in Ukraine, after Russia’s foreign minister said regions holding widely-criticized referendums would get full protection if annexed by Moscow…Votes in four eastern Ukrainian regions, aimed at annexing territory Russia has taken by force, were staged for a third day on Sunday. The Russian parliament could move to formalize the annexation within days…By incorporating the areas of Luhansk, Donetsk, Kherson and Zaporizhzhia into Russia, Moscow could portray efforts to retake them as attacks on Russia itself, a warning to Kyiv and its Western allies.