U.S. Kerry calls for calm as leaders implement Brexit vote

U.S. Secretary of State John Kerry arrives to address a joint news conference with European Union foreign policy chief Federica Mogherini (unseen) after their meeting the EU Commission headquarters in Brussels, Belgium, June 27, 2016. REUTERS/Francois Lenoir

LONDON/BRUSSELS (Reuters) - It is important that "nobody loses their head" as the European Union and the United Kingdom grapple with the effects of a referendum in which Britons voted to leave the 28-nation bloc, U.S. Secretary of State John Kerry said on Monday.

Britain's referendum last week to leave the bloc sent global stocks tumbling and dealt an unprecedented blow to Europe's post-World War Two order, while triggering a political meltdown in Britain itself, with the ruling Conservatives and opposition Labour Party both in disarray.