Outgoing British Prime Minister David Cameron said on Tuesday he wanted a "constructive" divorce from the European Union after last week's Brexit referendum and hoped for "the closest possible" ties when London leaves the 28-nation bloc.
"While we are leaving the European Union; we mustn't be turning our back on Europe. These countries are our neighbors, our friends, our allies, our partners," Cameron said on arriving in Brussels for a summit with other EU leaders dominated by Brexit. "And I very much hope we'll seek the closest possible relationship in terms of trade and cooperation and security, because that is good for us and that is good for them."
European Council President Donald Tusk told reporters that only London could file the formal notification that would start the two-year divorce process.
"This is the only legal way we have ... which means that we also have to be patient," he said. "Without the notification form the UK, we will not start any negotiations on the divorce process or the future relations."
WATCH: Britain Votes to Leave EU in Brexit Vote
Tusk said 27 other EU leaders would meet on Wednesday without Cameron to discuss Brexit would also start talks on reforms needed in the bloc to keep it together after the historic blow.
European countries are particularly worried about the impact on the rest of the European Union of the uncertainty created by Britain's vote to leave, with little idea of when, or even if, the country will formally declare it is quitting.
Britain faced angry calls from other European leaders to act quickly to resolve the political and economic chaos unleashed by its vote to leave the European Union, which the International Monetary Fund said could put pressure on global growth.
Financial markets recovered slightly on Tuesday after the result wiped a record US$3 trillion off global shares and sterling fell to its lowest level in 31 years, but trading was volatile and policymakers vowed to take all necessary measures to protect their economies.
British finance minister George Osborne, whose attempt to calm markets fell on deaf ears on Monday, said he would have to cut spending and raise taxes to secure fiscal stability after a third credit ratings agency downgraded the country's debt.
Firms have announced hiring freezes and possible job cuts, dashing voters' hopes the economy would thrive outside the EU.
Cameron, who resigned after it became clear he had failed in his efforts to persuade the country to stay in the EU in the referendum, which he called, says he will leave it to his successor to formally declare Britain's exit.
His party says it aims to choose a new leader by early September, but those who campaigned for Britain's leave vote have made clear they hope to negotiate a new deal for the country with Europe before triggering the formal exit process. European leaders have said that is not an option.
"No notification, no negotiation," Juncker said.