German chancellor Angela Merkel has said it must the goal for the European Union to maintain "close future relations" with Britain as she confirmed she will hold a summit of leaders on Monday.
Mrs Merkel said she will meet with the European Council president Donald Tusk, French president Francois Hollande and Italy's prime minister Matteo Renzi in Berlin on Monday.
The German leader said she "deeply regrets" the decision of a majority of British voters at the ballot box to split from the 28-member bloc.
But amid apparent anxiety from other leaders, she said Europe needs to stay "calm and composed" in the wake of Britain's exit.
Foreign Secretary Philip Hammond said there will have to be a "trade-off" on UK access to the EU single market and migration controls.
France's foreign minister called for the UK to trigger the exit clause after a meeting with counterparts of the six EU founding states.
European leaders have reacted to the UK's historic vote to leave the EU.