Brexit: Europe to push for quickie British divorce as John Kerry joins in discussion

German Chancellor Angela Merkel will host the leaders of France, Italy and the European Union in Berlin on Monday

European leaders embark this week on a frantic drive to push Britain into a quick divorce, with top US diplomat John Kerry rushing to join discussions as the "Brexit" crisis goes global.

Germany's powerful Chancellor Angela Merkel will host the leaders of France, Italy and the European Union in Berlin on Monday amid fears Britain's vote to leave will create a domino effect in eurosceptic member states.

In what promises to be one of the bitterest summits in the EU's history, British Prime Minister David Cameron will then face huge pressure in Brussels tomorrow to immediately trigger the two-year exit process.

But Cameron, who has said he will resign by October and leave the negotiations to his successor, is not expected to trigger the Article 50 mechanism to leave the EU when he meets his European peers, a senior bloc official said.

The British premier is to be left out in the cold on the second day of the summit on Wednesday when the other 27 EU leaders meet without him.

With a dismayed Washington fearing key ally Britain's decision to leave the EU will harm Western unity, Kerry flies in to Brussels and London on Monday.

"An EU united and strong is our preference for a partner to be able to work on the important issues that face us today," Kerry said after talks in Rome with Italian Foreign Minister Paolo Gentiloni.

"Brexit and the changes that are now being thought through have to be thought through in the context of the interests and values that bind us together with the EU," he added.

For European powers the priority is to divorce as soon as possible and stabilise a union that is already struggling with growing anti-EU populism, a migration crisis and economic woes.

Merkel has said there was "no reason to be nasty" in Britain's exit negotiations.

But there are increasing fears in London that an impatient EU will want to make an example of Britain to discourage others thinking about a referendum of their own.

Sources in the French presidency said Merkel and Francois Hollande spoke by phone Sunday and were "in full agreement on how to handle the situation" created by the referendum outcome.

Both leaders "want the greatest clarity to avoid any uncertainty" after the Brexit vote, said a source close to Hollande.

Merkel and Hollande will hold further talks when they meet in Berlin on Monday for talks that will also include Italian Prime Minister Matteo Renzi.