LONDON (Reuters) - Royal Bank of Scotland <RBS.L> Chief Executive Officer Ross McEwan has warned staff that Britain's decision to leave the European Union has caused a range of economic uncertainties "in the short, medium and long term", a memo seen by Reuters showed.

Although he said the result was a surprise for many, McEwan said the state-backed bank has planned extensively for both outcomes to ensure it was well placed to support customers and colleagues.

New Zealand-born McEwan also paid tribute to the RBS staffers in all parts of the lender who managed the immediate market fallout that followed the result on Friday, who he said "did us all proud."

He also noted that the result had rippled beyond markets and into "everyday exchanges between colleagues, friends and family" but called on RBS employees to remember how diversity was a major contributor to the bank's success.

"As someone born outside the UK, I see one of this country's biggest strengths as its openness to the rest of the world, and the people of it. As a major employer and backer of the economy we have a duty to ensure that we reflect that," he said.

"The diversity of those who make up this bank at every level is key to our success. In uncertain times I want to ensure that everyone understands that."

Shares in RBS have fallen by 27.5 percent in the three days since the decision after earnings downgrades and sell off by worried investors.

(Reporting By Andrew MacAskill, editing by Sinead Cruise)