Donald Tusk, President of the European Council, said the EU would not be "intimidated" by threats from Britain that it would prefer to walk away from Brexit talks if it did not get its way.
British Prime Minister Theresa May is expected to trigger Article 50 by the end of this month. That would allow formal negotiations to begin between the British government and the 27 member states on the terms of the UK's exit from the EU.
"It is our wish to make this process constructive, and conducted in an orderly manner," Tusk said in a statement to the European Parliament.
"However, the claims, increasingly taking the form of threats, that no agreement will be good for the UK, and bad for the EU, need to be addressed.
"I want to be clear that a 'no deal scenario' would be bad for everyone, but above all for the UK, because it would leave a number of issues unresolved.
"We will not be intimidated by threats, and I can assure you they simply will not work. Our goal is to have a smooth divorce and a good framework for the future. And it is good to know that Prime Minister Theresa May shares this view."
'Brexit bill' to become law
The bill that allows the UK government to trigger Article 50 is expected to receive royal assent and become enshrined in British law on Thursday.
The timetable was overshadowed by an intervention from Scottish First Minister Nicola Sturgeon
, who demanded a new independence referendum for Scotland on Monday.
On Tuesday, May told the House of Commons that Britain was facing a "defining moment" as it prepared to leave the EU.
But there remains a lack of clarity over the government's position on trade deals and tactics over withdrawing from the bloc.
Brexit Secretary David Davis admitted hat that British government had not yet carried out an assessment of what leaving the EU without a deal would have on the economy.
When asked at a parliamentary committee hearing whether an assessment had been carried out, Davis said: "If you mean under my time, no."
Davis also suggested that claims that a 'no deal' scenario "is not as frightening as some people think" but said he would be able to give a more accurate forecast in a year's time.
Pressure on May
Davis' statement is likely to increase the pressure on May's government with tension already rising ahead of the triggering of Article 50.
Last week, lawmakers published a report
which warned that the government's failure to prepare for a scenario in which no deal is reached with the EU Union over Brexit would be a "serious dereliction of duty."
The House of Commons Foreign Affairs Committee said the United Kingdom should be prepared for the "real prospect" that the two-year negotiation cycle may end in deadlock.
"The possibility of 'no deal' is real enough to require the government to plan how to deal with it," head of the committee Crispin Blunt said in the report.
"But there is no evidence to indicate that this is receiving the consideration it deserves or that serious contingency planning is under way. The government has repeatedly said that it will walk away from a 'bad' final deal. That makes preparing for 'no deal' all the more essential," he added.