(Reuters) - Ukraine's President Volodymyr Zelenskiy told UK Prime Minister Boris Johnson by telephone on Sunday that the next 24 hours are crucial for Ukraine, a Downing Street spokesperson said.

       Johnson said the UK and its allies would do everything possible to guarantee that defensive aid reached Ukraine, the spokesperson said in a statement.

       (Reporting by Shivani Tanna in Bengaluru; Editing by Daniel Wallis)