The European Council president said Tuesday that the bloc's "hearts are still open" to the U.K. if it changes its mind about Brexit.
Donald Tusk's remarks at the European Parliament's plenary sitting in Strasbourg city came amid a new debate in the U.K. on whether to hold a second referendum on leaving the EU.
Also, in an EU summit last December EU leaders had agreed that "sufficient progress" has been made in the Brexit negotiations to move on to phase two, which includes talks on the future relations between the EU and the U.K.
Tusk called for "more clarity" from British Prime Minister Theresa May over her plans for what relationship it wants with the EU after Brexit takes effect.
He said Brexit was due to happen in March 2019 "unless there is a change of heart among our British friends".
"Wasn't it David Davis himself who said: "If a democracy cannot change its mind, it ceases to be a democracy?" he said, referring to the Brexit secretary.
"We, here on the continent, haven't had a change of heart. Our hearts are still open to you."
European Commission President Jean-Claude Juncker repeated to the MEPs Tusk's message that the EU's "door still remains open" to the UK, and hoped it "will be heard clearly in London".
The second phase of Brexit negotiations, which will shape the future trade relations between the U.K. and the bloc will begin in March.
Britain is set to leave the EU in March 2019 but the sides have agreed on principle to introduce a transition period expected to last for around two years.
