By Steve Holland, Guy Faulconbridge and Dmitry Antonov WASHINGTON/LONDON/MOSCOW (Reuters) – The United States and Britain are prepared to punish Russian elites close to President Vladimir Putin with asset freezes and travel bans if Russia enters Ukraine, Washington and London said on Monday as tensions also spilled over at the United Nations. Britain urged Putin to “step back from the brink” after the Russian buildup of troops near Ukraine stoked fears of war, and warned any incursion would trigger sanctions against companies and people close to the Kremlin. “The individuals we have identified…