The German Chancellor, Angela Merkel, has said there can be no talks on Brexit before the UK formally begins the process of leaving the EU.
While accepting the UK needed time, she added it should not be a "long time".
Mrs Merkel is due to meet the French president and Italian prime minister later in Berlin, with the speed of negotiations for the UK's exit high on the agenda.
The UK's chief finance minister issued a statement to try to calm markets.
UK shares have remained uneasy in the wake of the vote, although Chancellor George Osborne's statement appeared to have helped lessen further big falls in shares and the pound.
US Secretary of State John Kerry has said his country's "special relationship" with the UK will be maintained.
"The vote did not come out the way US President [Barack] Obama and I had expected but that's democracy," he told reporters in Brussels.
Last Thursday, the UK voted 52-48 in favour of leaving the EU.
"The reality is that a majority of British citizens voted to leave… so I await a communication about Article 50 from the UK addressed to the EU," Mrs Merkel said.