The comments came as British Prime Minister Theresa May made a diplomatic push in Brussels, where she was meeting with top European Union officials in an effort to break an impasse, especially in the thorny issue of the Irish border.
May met with EU Commission President Jean-Claude Juncker and will later speak with EU Council President Tusk amid hopes of progress on the divorce issues: Britain's exit bill, the Irish border and the rights of citizens. Only then will the EU agree to move on discuss future relations, including trade.
Tusk said a breakthrough had come in the talks on the Irish border, as reported to him by Irish Prime Minister Leo Varadkar.
"Tell me why I like Mondays!" Tusk wrote in an optimistic Twitter message after his phone call with Dublin. "Getting closer to sufficient progress," he said. "Sufficient progress" is short for what the EU wants to see on the divorce issues before trying to get a new trade deal ahead of Britain's official departure on March 29, 2019.
The 27 other EU leaders will decide at a summit on Dec. 14-15 whether those preconditions have been met.
The breakthrough under discussion would allow for the border between the EU's Ireland and the U.K.'s Northern Ireland to remain transparent for trade. Both sides would promise to keep the trading rules compatible.
"Basically the British government would commit to maintain the full alignment of legislation where pertinent," said Belgian member of the European Parliament Philippe Lamberts.
Lamberts said he was "optimistic that the European (summit) can now agree to move discussion on to the UK's future relationship."
"It seems the British government is now coming to terms with reality," he said.
May's government has long said there will be no "hard border" with Ireland once Britain leaves the EU's tariff-less single market and the customs union, a looser trading bloc that includes non-EU states like Turkey. Ireland and other EU countries are insisting the U.K. provide details of how customs checkpoints and other border obstacles can be avoided.
One solution would be to allow Northern Ireland to stay in the customs union when the rest of the U.K. leaves. But that would be unacceptable for Northern Ireland's Democratic Unionist Party - upon which May's minority government relies on to stay in power.
Diplomats have been negotiating relentlessly over the past days to meet an EU-imposed deadline of Monday to find "sufficient progress" on the divorce issues.
The European Parliament's chief Brexit official said it was "50/50 to have something." Guy Verhofstadt added that a financial settlement on the divorce was as good as done - "it seems, yes" - while the talks on citizens' rights and Ireland's border still had outstanding issues to solve.
Yet Monday was still fraught with difficulties. Juncker first met with Brexit experts from the European Parliament, which will eventually have to endorse any departure deal.
And Verhofstadt warned that unless all issues are solved "there will be no green light in October 2018." A decision on any new deals with Britain would have to be reached by the fall of next year to give individual member states enough time to approve all the measures in their parliaments before the final date on March 2019.
Jill Lawless contributed from London
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