By David Hughes, PA Political Editor
Boris Johnson has been met with a wall of resistance from Brussels over his demand for major changes to the Withdrawal Agreement, increasing the risk of a no-deal Brexit.
The Prime Minister said that the backstop - the contingency plan to avoid a hard border with Ireland - should be removed from the divorce deal ahead of the October 31 Brexit deadline.
But European Council president Donald Tusk defended the measure and warned that scrapping it risked a return to a hard border on the island of Ireland.
Downing Street said that unless the backstop is abolished "there is no prospect of a deal".
Mr Tusk said: "The backstop is an insurance to avoid a hard border on the island of Ireland unless and until an alternative is found.
"Those against the backstop and not proposing realistic alternatives in fact support reestablishing a border. Even if they do not admit it."
Officials in Brussels privately accused Mr Johnson of making "incorrect" and "misleading" claims about the situation.
In public comments, the European Commission said the Prime Minister had failed to put forward a "legal, operational solution" to the issue and had acknowledged that if one could be found it might not be ready in time.
Mr Johnson wrote to Mr Tusk on Monday outlining his opposition to what he called the "anti-democratic" Northern Ireland backstop, claiming it risked undermining the Good Friday Agreement.
In his letter, Mr Johnson said while he wants the UK to leave the EU with a deal, he could not support a Withdrawal Agreement that "locks the UK" into a potentially indefinite customs union and applies single-market legislation in Northern Ireland.
As an alternative to the backstop, the Prime Minister said the UK would agree to a "legally binding commitment" not to put in place infrastructure, checks or controls at the border with Ireland and would hope the EU did the same.
The backstop should be replaced with a commitment to put in place "alternative arrangements", as far as possible before the end of the transition period, as part of the future relationship between the UK and EU.
But European Commission spokeswoman Natasha Bertaud said the letter "does not provide a legal, operational solution to prevent the return of a hard border on the island of Ireland".
"It does not set out what any alternative arrangements could be and in fact it recognises that there is no guarantee that such arrangements will be in place by the end of the transitional period," she said.
An official briefing note circulated among diplomats from the member states made clear the EU's frustration with Mr Johnson's approach.
The document, seen by the PA news agency, disputes Mr Johnson's claims about the Good Friday Agreement and the Irish border.
It was "incorrect to state that the people of Northern Ireland have no influence over the legislation that would apply to them" and "misleading" to suggest that the two separate jurisdictions that exist on the island can be managed with an open border because that was only possible now due to the framework provided by EU law.
Any attempt to remove the "vital insurance policy" of the backstop would also be rejected by MEPs, the European Parliament's Brexit co-ordinator Guy Verhofstadt indicated.
"The time for bluster & political blame games is fast running out," he added.
In the face of apparently co-ordinated resistance from the three main EU institutions - the European Council, the European Commission and the European Parliament - Mr Johnson stood firm on the need for change.
"It is clear that unless the Withdrawal Agreement is reopened and the backstop abolished there is no prospect of a deal," a Downing Street spokesman said.
"It has already been rejected three times by MPs and is simply unviable as a solution, as the PM's letter makes clear."
Mr Johnson will meet German Chancellor Angela Merkel on Wednesday and France's Emmanuel Macron on Thursday for his first face-to-face talks with Europe's key powerbrokers.
The latest row with Brussels comes as a senior US politician warned that legislators would move to block a future US-UK trade deal if it puts the Good Friday Agreement at risk by introducing a hard border.
US Senate Democratic leader Chuck Schumer has written to US Secretary of State Mike Pompeo warning that Congress could work on a cross-party basis to block a deal.
Mr Johnson spoke to US President Donald Trump on the phone on Monday night to update him on Brexit ahead of their meeting at the G7 summit in France at the weekend.
Mr Trump later said he and Mr Johnson had shared a "great discussion" in which they talked about moving "rapidly on a US-UK free trade deal" after Britain's departure from the bloc.