Ahead of hours for the U.K. to leave the EU officially, the head of European Commission said the bloc "is looking for the best relationship with the U.K."
"But, it will never be as good as membership," Ursula von der Leyen told a joint news conference on Brexit and the future of the EU.
European Council's head Charles Michel and President of European Parliament David Sassoli were accompanying her in Brussels.
The U.K., which has been a member of the EU since 1973, is set for a formal departure from the bloc on Friday at 11 p.m. (2300GMT) in London or midnight in Brussels as per the 2016 referendum.
Von der Leyen and heads of the bloc's other major institutions expressed their regrets for the British people's decision but urged to move on "to a new chapter".
"We have tried all to convince them about the advantages of being together," Sassoli said.
Then both von der Leyen and Michel stressed that the EU would focus on the challenges of climate action and digitalization in order to enhance economic growth.
All three also implied that the U.K. needed to prepare for tough negotiations on the economic relations with the EU, "a global economic powerhouse".
"Strength doesn't lay in splendid isolation, but in unified cooperation," said von der Leyen, referred to the motto of the 19th century Britain's foreign policy, while praised the EU history for working together.
Michel assured that the EU wanted to have "as tightest relations as possible" with the U.K., but also warned that London needed to decide if "it wanted to diverge from EU regulation or have full access to the single market."
In the upcoming 11-month transition period, the U.K. and the EU are supposed to agree on the terms of economic cooperation.
British Prime Minister Boris Johnson favors a scenario in which British goods and services can enter the EU market without any tariffs or quotas while the U.K. stops fully complying with EU rules.
But the EU rejects the plan as it will give more power to the country leaving the bloc than to those who remain.
