Britain will "regret" leaving the EU, European Commission President Jean-Claude Juncker said on Wednesday.
Delivering his annual state of the union address here, Juncker said Brexit would be a "sad, tragic" moment for the EU but that the 27-member union would "move on", BBC reported.
"We will always regret this. I think you will regret it as well soon, may I say."
"Brexit is not the future of Europe. It is not the be all and end all," Juncker said.
Juncker unveiled plans for a summit to be held on March 30, 2019 -- the day after Britain leaves the EU -- to map out the future of the bloc.
He called for closer economic and defence co-operation among member states, including more support for states outside the eurozone and reforms to the single market.
Reflecting on the economic and political challenges that the continent had faced in recent years, he said the "wind is back in Europe's sails".
He also used the speech to spell out a major reform package for the EU: with a new push for all applicable member states to join the Euro, the expansion of the borderless Schengen area to Romania and Bulgaria, as well as the merger of the presidencies of the European Commission and European Council, the Independent reported.
Juncker also backed the creation of a new European economics and finance minister as well as reforms to the European Parliament that would see some MEPs elected from European-wide lists voted on by all countries at once.
Speaking in the same debate, former UK Independence Party (UKIP) leader Nigel Farage said the EU had "learnt nothing" from Brexit and was ploughing "full steam ahead".
Farage, the best known campaigner in the Parliament for the UK's withdrawal from the EU, attacked what he said were "truly worrying" plans to create a single President of the EU, an EU Finance Minister and a "strong EU army in a militarised Europe".
He said what was being proposed was "more Europe in every single direction without the consent of the people".
Negotiations between the UK and EU are continuing although the latest round of talks, due to begin on Monday, have been put back a week to allow "more time for consultation".
Speaking on Tuesday, former Brexit Minister Lord Bridges said the UK must be "honest" about the "complexity and scale" of leaving the EU as well as the lack of time to reach agreement with the EU.