And at the end of their press conference, Mr Varadkar was picked up by the microphones telling Mr Tusk: "They'll give you awful trouble in the British press for that".
Mr Tusk made his remarks during a press conference alongside Taoiseach Leo Varadkar and a day before Prime Minister Theresa May is to fly to Brussels for talks.
Since British lawmakers voted down the withdrawal agreement last month, parliament has instructed May to replace its most contentious element - an insurance policy covering the possible future arrangements for the border between EU-member Ireland and the British province of Northern Ireland. "We will not gamble with peace or put a sell-by date on reconciliation", Tusk said.
"This 29 March deadline is a deadline set in Britain by Britain and it is open to the United Kingdom to request an extension to Article 50, provided there's a objective to that, or to revoke Article 50 if that's their wish".
While Mr Varadkar met the EU's leaders, Mrs May held meetings with all five of the main Northern Irish parties at Stormont House in Belfast.
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Failing that, they will join the United States in recognizing National Assembly speaker Guaido as Venezuela's interim president. Francisco Yanez, a member of the air force's high command, calls on other members of the military to defect. "Wives are sacred.
The British prime minister is due in Brussels on Thursday to seek a way to ensure Britain's orderly withdrawal from the European Union and avoid what Tusk warned would be a "fiasco".
The "top priority" for the bloc was to "maintain the peace process in accordance with the Good Friday Agreement", Tusk said.
May is signaling she will seek changes to the deal rather than the outright removal of the controversial Irish border provision, which has so alarmed many Brexiters in the U.K. Parliament.
She told an audience of business leaders and journalists that she wanted to "affirm my commitment to delivering a Brexit that ensures no return to a hard border between Northern Ireland and Ireland, which is unshakeable. It's a European issue and that's why we cannot accept the idea that the withdrawal agreement could be reopened", Juncker said, adding that the backstop was part of the November agreement.
However, Mr Tusk is unfazed and laughs: "I know".
Tusk said he hopes she will bring to Brussels "a realistic suggestion on how to end the impasse".
Ministers are hoping European Union will agree to a two-month "grace period" after 29 March in case Prime Minister Theresa May's deal passes through parliament to provide the additional time for necessary legislation, the report said.