By Guy Faulconbridge and Dmitry Antonov LONDON/MOSCOW (Reuters) – Britain urged Russian President Vladimir Putin on Monday to “step back from the brink” over Ukraine, warning that any incursion would trigger sanctions against companies and people with close links to the Kremlin. The United States and Britain are trying to signal to Putin that Russia’s richest men, who have huge assets abroad, will face punishment if he orders troops to invade Ukraine, though Moscow has repeatedly denied that it wants a war with its fellow former Soviet neighbour. The United States and its allies have prepared …