Tusk, the president of the European Council, tweeted that "we will not renegotiate the deal, including the backstop, but we are ready to discuss how to facilitate U.K. ratification." He said that "as time is running out, we will also discuss our preparedness for a no-deal scenario."
EU leaders were already scheduled to meet in Brussels on Thursday and Friday to discuss migration and the bloc's future long-term budget, among other issues.
A key member of the European parliament's Brexit team says that British Prime Minister Theresa May's Brexit strategy has turned into "a game of hide and seek" which will fail to force the EU to renegotiate the U.K. withdrawal deal.
Green MEP Philippe Lamberts told The Associated Press that, despite May's claim to seek additional reassurances to the U.K. deal with the EU that has been already struck, there would be no changes awaiting her at Thursday's EU summit.
Lamberts said that "we are fully behind negotiator Michel Barnier but he has been very clear: if you want Brexit, the deal is on the table and there will be no other deal."
Apart from EU member states, the European Parliament also needs to approve the U.K. withdrawal deal.
British opposition leader Jeremy Corbyn has challenged Prime Minster Theresa May's decision to delay a vote on Brexit in the House of Commons, arguing that her government is in "complete disarray."
Labour lawmakers shouted "Resign! Resign!' as May wrapped up her remarks Monday, adding further insult to the humiliation of failing to deliver on her signature piece of legislation, the Brexit divorce deal from the European Union.
Corbyn described the situation as unprecedented and serious. He says "the government has lost control of events and is in complete disarray."
Even members of May's own party were quick to further criticize the way she's handled the negotiations.
Conservative Party lawmaker Jacob Rees-Mogg sharply rejected May's "undeliverable deal," saying it risked paving the way for a Labour Party government led by Corbyn.
The pound has fallen further after British Prime Minister Theresa May canceled a vote on her Brexit deal and struck a defiant tone in an address to parliament.
The British currency, which is the main gauge of international investors' confidence in the country's economy, fell to a 20-month low of $1.2515, down a sharp 1.7 percent on the day.
The main British stock index usually gets a boost from a weaker currency, as it helps the earnings of the many multinationals listed on it. But the FTSE 100 was also down, by 0.5 percent on the day, underscoring the depth of investors' concern.
Investors are worried that the political gridlock in Britain over how to leave the EU is increasing the likelihood of the country exiting the bloc without a deal on future relations. That is a worst-case scenario, the Bank of England says, that could lead to the deepest recession in about a century and a further plunge in the pound.
British Prime Minister Theresa May told lawmakers that government was stepping up its preparations for a no-deal Brexit.
May told lawmakers that while her Brexit deal with the European Union was still "the best deal that is negotiable," and insisted that any deal would require compromise. But nonetheless, she says the government must be prepared for the potential that the country would exit without a deal.
May says "for as long as we fail to agree a deal, the risk of an accidental 'no deal' increases."
May's comments came after she postponed a vote scheduled for Tuesday on the EU divorce deal, acknowledging she would have lost by a "significant margin."
British Prime Minister Theresa May says her Brexit divorce deal with the European Union is still "the best deal that is negotiable," as she aimed to win Parliament's support.
In a stinging statement Monday to the House of Commons, May reminded lawmakers that any Brexit deal would require compromise.
She then asked whether or not the House of Commons really wanted to deliver Brexit — and if it was willing to re-open the political division within the country by challenging the 2016 vote of the British people to leave the bloc.
May's comments came after she postponed the vote in parliament on her EU divorce deal, acknowledging she would have lost Tuesday's vote by a "significant margin." The decision throws her Brexit plans into chaos.
British Prime Minister Theresa May has postponed Parliament's vote on her European Union divorce deal to avoid a shattering defeat — a decision that throws her Brexit plans into chaos.
All signs had pointed to a big defeat for the prime minister in the vote planned for Tuesday. But postponing the vote is a fresh humiliation for May, who became prime minister after Britain's 2016 decision to leave the EU.
May has been battling on Brexit ever since — first to strike a divorce deal with the bloc, then to sell it to skeptical British lawmakers before the U.K. leaves the bloc on March 29.
Both Conservative and opposition Labour Party lawmakers have said they would not back the divorce deal that May and EU leaders agreed on last month.
The foreign minister of Belgium says the European Union might be willing to modify minor details of its Brexit agreement with the U.K. but that wholesale changes are out of the question.
Foreign Minister Didier Reynders told reporters in Brussels that it's always "possible to discuss about some details but we (know) the limits and the red lines of the European Union."
But he added: "it is quite difficult to change important elements."
Reynders said he is "quite pessimistic" about the future of Brexit given developments in London.
He said he wants to hear exactly what Prime Minister Theresa May wants and that things would be clearer after she addresses the U.K. Parliament Monday.
The Dutch foreign minister says the European Union would study any new Brexit offer that British Prime Minister Theresa May makes but that chances are slim it would be accepted.
Minister Stef Block spoke in Brussels before May was due to address the British parliament on Monday afternoon about the divorce deal between Britain and the EU and was unaware of exactly what she might announce.
He says "of course we will look carefully at any proposal she might make."
Blok added: "But we know how difficult it has been to reach agreement. So if there will be talks, it won't be easy."
The House of Commons in London is due to vote Tuesday on whether to accept or reject the Brexit deal, and signs point to a big defeat for May's Brexit deal.
British Prime Minister Theresa May will make an emergency statement to Parliament about Brexit, amid reports that a crucial vote on her EU divorce deal will be postponed.
The House of Commons Speaker's office says May will make the previously unscheduled statement at about 3:30 p.m. (10:30 a.m. EST).
The announcement came as May held talks with her Cabinet about the next steps in the Brexit process. The House of Commons is due to vote Tuesday on whether to accept or reject the Brexit deal, and signs point to a big defeat for the prime minister.
May's office said the vote was definitely going ahead, but the BBC and other outlets reported it would be delayed.
The European Union's top court has ruled that Britain can change its mind over Brexit, boosting the hopes of people who want to stay in the EU that the process can be reversed.
The European Court of Justice ruled Monday that when an EU member country has notified its intent to leave, "that member state is free to revoke unilaterally that notification."
Britain voted in 2016 to leave the 28-nation bloc, and invoked Article 50 of the EU's Lisbon Treaty in March 2017, triggering a two-year exit process. Article 50 contains few details, in part because the idea of any country leaving was considered unlikely.
The Luxembourg-based ECJ said that given the absence of any exit provision in Article 50, countries are able to change their mind in line with their own constitutional arrangements and that such a move "reflects a sovereign decision."
The British government is free to do so as long as no withdrawal agreement has entered force.
Lawless reported from London.