(Reuters) - Russian President Vladimir Putin on Friday questioned why British Prime Minister David Cameron had called a referendum on Britain's membership of the European Union.

"If it's such a problem, why did he initiate this, if he is against it himself?" Putin said of Cameron at a meeting on the sidelines of the St Petersburg International Economic Forum.

Putin said that he had a view on whether Britain should leave the EU but that it was not appropriate for him to voice it because it was Britain's internal affair.

(Reporting by Alessandra Galloni; Writing by Christian Lowe; Editing by Hugh Lawson)