Theresa May has accused European politicians and officials of seeking to influence the result of the UK's General Election as the war of words over Brexit intensified.
The Prime Minister used a Downing Street statement to claim that the UK's position had been misrepresented and the European Commission's position had hardened.
"The events of the last few days have shown that whatever our wishes and however reasonable the positions of Europe's other leaders, there are some in Brussels who do not want these talks to succeed, who do not want Britain to prosper," she said.
In a statement after meeting the Queen to mark the dissolution of Parliament, Mrs May said the victor of the June 8 election would face "one overriding task", getting the "best possible deal" for the UK.
"In the last few days we have seen just how tough these talks are likely to be," she said.
"Britain's negotiating position in Europe has been misrepresented in the continental press. The European Commission's negotiating stance has hardened.
"Threats against Britain have been issued by European politicians and officials.
"All of these acts have been deliberately timed to affect the result of the General Election that will take place on June 8."
Mrs May warned of "serious consequences" if Brexit negotiations went wrong.
She said: "If we do not get this right, the consequences will be serious and they will be felt by ordinary working people across the country.
"This Brexit negotiation is central to everything.
"If we don't get the negotiation right, your economic security and prosperity will be put at risk and the opportunities you seek for your families will simply not happen.
"If we do not stand up and get this negotiation right we risk the secure and well-paid jobs we want for our children and our children's children too.
"If we don't get the negotiation right, if we let the bureaucrats of Brussels run over us, we will lose the chance to build a fairer society with real opportunity for all."
Mrs May said voters faced a "very simple" choice on June 8 between her and Jeremy Corbyn.
"With me you will get strong and stable leadership and an approach to Brexit that locks in economic growth, jobs for our children and strong finances for the NHS and the country's schools," she said.
"Or you will get Jeremy Corbyn with a hung parliament and a coalition of chaos.
"Britain will simply not get the right Brexit deal if we have the drift and division of a hung parliament.
"So, with Jeremy Corbyn negotiating Brexit, we will all pay a high price."
Mrs May said that the election was not only about Brexit, but also about building a stronger and fairer economy and protecting the UK against attacks from extremists and efforts by separatists to tear it apart.
"As we face this critical time for our country - five years that will determine the course of the United Kingdom for generations to come - we must do so together, with a unity of purpose to make a success of Brexit and to build a stronger, more secure country too," she said.
Mrs May said she would have a "clear message" in the election campaign.
"If like me you believe in Britain, if like me you want our country to succeed, if like me you believe in putting division behind us, in looking to the future and getting on with the job of building the stronger, more secure country that we need, then fix your sights on the future and in this unique and crucial election for our country, give me your backing to lead Britain.
"Give me your backing to speak for Britain, give me your backing to fight for Britain, give me your backing to deliver for Britain a stronger Britain where economic progress is secured and prosperity and opportunity is shared by all.
"A Britain that works not just for the privileged few but for every single one of us."
Mrs May said she had made clear to Brussels in her letter formally starting the Brexit process that "in leaving the European Union, Britain means no harm to our friends and allies on the continent".
"We continue to believe that no deal for Britain is better than a bad deal, but we want a deal," she said.
"We want a deep and special partnership with the EU and we want the EU to succeed."
Leaks from a Downing Street dinner in which Mrs May hosted European Commission president Jean-Claude Juncker and Brexit negotiator Michel Barnier have revealed the tensions between the two sides.
Mr Juncker reportedly left saying he was "10 times more sceptical" about the prospect of a deal.
Mrs May said the events of recent days showed "now more than ever we need to be led by a prime minister and a government that is strong and stable".
"Because making Brexit a success is central to our national interest and central to your own security and prosperity," she told voters.
"If we do not get this right, the consequences will be serious."
SNP leader Nicola Sturgeon criticised Mrs May's speech on Twitter, saying: "UK needs best possible Brexit deal and has limited leverage, so for PM to poison atmosphere for partisan reasons is deeply irresponsible.
"Having called election for reasons of party not national interest, PM now seems intent on fighting campaign in same way.
"Making a bogeyman of EU is all about distracting attention from Tories' wider record - while PM continues to hide from voters."
Labour's Chuka Umunna, a leading supporter of the Open Britain campaign, accused Mrs May of "straightforward, crude electioneering".
He added: "This is straight out of the Donald Trump playbook - not what we expect from a British Prime Minister."
Scottish Labour's Europe spokesman Lewis Macdonald MSP said: "Theresa May has gone full Donald Trump with this bizarre intervention.
"This Tory government is clearly woefully under-prepared for the difficult and complicated negotiations ahead - and insulting Europe's political leaders is unlikely to make them any more amenable to giving the UK a good deal.
"The Tories' handling of Brexit has so far been a disaster.
"Labour would rip up Theresa May's Brexit white paper and put protecting workers' rights and having access to the single market at the heart of negotiations."
Labour leader Mr Corbyn said: "Theresa May is playing party games with Brexit in the hope of winning advantage for the Tories in the General Election.
"By winding up the public confrontation with Brussels, the Prime Minister wants to wrap the Conservative Party in the Union Jack and distract attention from her Government's economic failure and run-down of our public services.
"But Brexit is too important to be used as a political game in this election.
"These are vital negotiations for every person in Britain and for the future of our country.
"But Theresa May is putting party interest ahead of the national interest.
"The Prime Minister is right that there are those in Brussels who don't want a deal.
"But that is also true of leading figures in the Tory party, who want to use Brexit to turn Britain into a low-wage tax haven.
"The Prime Minister says that no deal would lead to a different economic model for Britain.
"In plain terms, that means wiping out employment rights and consumer protections and giving still more tax breaks to the rich and big corporations.
"That's the threat and the risk that comes from this Tory Government.
"Only Labour can be trusted to negotiate a Brexit deal that puts jobs and living standards first.
"Labour will negotiate a Brexit for the many, not the few."
Former Scottish first minister Alex Salmond said: "For the umpteenth time Theresa May is parroting the same line in this election.
"She needs a reminder that this is a democratic contest between people who disagree with her, not something to be disfigured by the language of Lynton Crosby.
"This is the same dog whistle playbook which rebounded so spectacularly in the contest for a London mayor when people saw through the attempt to smear opponents.
"Not only will the Scottish people see through it, they will be outraged that a Prime Minister is demeaning herself and the campaign by reciting Crosby's lines."
Mr Juncker's chief of staff Martin Selmayr indicated that the Commission president would welcome a result from the UK elections which provided a strong negotiator on the other side of the table for Brexit talks.
Asked whether he agreed that Mrs May was a "bloody difficult woman", Mr Selmayr said: "President Juncker said today that she is an impressive woman and that she is a very impressive negotiator.
"That's the way we have come to know her, and I don't think that's going to change.
"We need a very strong negotiator who unites the whole nation behind her and then in a very strong and tough way leads the negotiations."
Speaking to a press conference hosted by the Politico website in Brussels, Mr Selmayr acknowledged that the leaks of last week's dinner had created "a lot of havoc", but insisted that the EU side were treating the negotiations "professionally".
"Certainly there is much ado about this, but that doesn't change anything in principle for the President of the Commission, the EU and Michel Barnier," he said.
"We will be going about this very professionally."
Brexit negotiations would not be "a walk in the park", but he was sure that, as a "pragmatic" nation, the UK would conduct them "in good faith", he said.
And he added: "Brexit will never become a success, of course, because it is a sad and sorry event.
"But as I have set out, it can be managed in a professional and pragmatic way."
Mr Selmayr played down the extent to which Brexit will dominate EU activities in the coming months, insisting that Mr Juncker will be spending only about "half an hour a week" on the subject.
Brexit would only come to the forefront of EU debate every three or four months, he predicted.