Officials in Dublin and Brussels have ruled out UK Prime Minister Boris Johnson's request to strip out parts of the Brexit deal negotiated by his predecessor Theresa May.

Johnson wrote to European Council President Donald Tusk on Monday asking Brussels remove the Irish backstop from the withdrawal agreement, something it has repeatedly refused to consider.

Tusk responded Tuesday by accusing Johnson of seeking to reestablish a border between Ireland and Northern Ireland.

"The withdrawal agreement is not open for renegotiation and the backstop is not open for change," a European Union source told The Guardian.

Ireland's governing party, Fine Gael, also rejected Johnson's demands to remove the backstop, which is designed to avoid the emergence of border checks on the island of Ireland.

A Downing Street spokesperson said: "U nless the Withdrawal Agreement is reopened and the backstop abolished there is no prospect of a deal."

The exchange keeps the UK firmly on course for a no-deal Brexit in October.

European officials in Dublin and Brussels have immediately rejected UK Prime Minister Boris Johnson's new demand to renegotiate Britain's exit deal, ahead of his meetings later this week with German Chancellor Angela Merkel and French President Emmanuel Macron.

Johnson wrote to the European Council's president, Donald Tusk, on Monday demanding that the European Union drop the Northern Ireland backstop from the Brexit agreement.

He described the backstop — which seeks to avoid border checks between Northern Ireland and Ireland after Brexit — as "anti-democratic and inconsistent with the sovereignty of the UK" because it could keep the UK bound in the EU's customs union.

He instead suggested that "alternative arrangements "and technological solutions must be implemented at the Irish border in exchange for new unspecified "commitments" on the border from the UK.

On Tuesday, Tusk responded by accusing Johnson of seeking to re-establish an Irish border.

"The backstop is an insurance to avoid a hard border on the island of Ireland unless and until an alternative is found," he tweeted.

"Those against the backstop and not proposing realistic alternatives in fact support reestablishing a border.

"Even if they do not admit it."

Natasha Bertaud, the European Commission's deputy spokeswoman, confirmed that Tusk's tweet was written in response to Johnson's letter and that it reflected the commission's position.

"We take note of Prime Minister Johnson's letter," she said.

A Downing Street spokesperson said on Tuesday: "We are deeply invested in the peace, prosperity and security of Northern Ireland and always will be and we have been clear that we will never place infrastructure, checks, or controls at the border.

"But it is clear that unless the Withdrawal Agreement is reopened and the backstop abolished there is no prospect of a deal. It has already been rejected three times by MPs and is simply unviable as a solution, as the PM's letter makes clear.

"We are ready to negotiate, in good faith, an alternative to the backstop, with provisions to ensure that the Irish border issues are dealt with where they should always have been: in the negotiations on the future agreement between the UK and the EU."

Brussels sources ruled out any renegotiation to the withdrawal agreement, which contains the backstop.

"There was a 2-1/2-year negotiating process in which the EU compromised, including on the question of the backstop," a source told The Guardian on Monday evening.

"The withdrawal agreement is not open for renegotiation and the backstop is not open for change. A legally operable backstop to avoid a hard border remains central to the withdrawal agreement for the EU27."

'Newfound spin'?

Irish Taoiseach Leo Varadkar at a European Union leaders summit in Brussels Reuters

EU officials believe the backstop is needed to preserve the integrity of the European single market and to preserve the Irish peace settlement.

It was included in the withdrawal agreement struck between EU and UK officials last year — an agreement the UK Parliament rejected three times this year.

Ireland's governing party, Fine Gael, also rejected Johnson's demands to remove the backstop.

Sen. Neale Richmond, the party's spokesman on European affairs, said Johnson's description of the backstop as "anti-democratic" was "new found spin," tweeting that Johnson had voted for it as part of the withdrawal agreement earlier this year.

He said most people in Northern Ireland supported the backstop and claimed it protected, rather than threatened, the peace agreement.

Johnson spoke on the phone with Leo Varadkar, the Irish premier, for over an hour shortly before the letter was published, with the two leaders outlining their opposing perspectives on the need for the backstop.

The pair also agreed to meet in Dublin in early September.

The UK is scheduled to leave the EU on October 31, and Johnson has pledged to deliver Brexit with or without a deal, despite warnings from business leaders that trade disruption would cause severe problems for many firms.

Some MPs believe Johnson's demands for concessions from the EU are so unrealistic that he is actively seeking no deal.

He insisted in the letter, however, that he was hoping to secure a negotiated deal with Brussels.

"You have my personal commitment that this government will work with energy and determination to achieve an agreement," he wrote. "That is our highest priority."

Johnson is scheduled to meet with Merkel in Berlin on Wednesday and with Macron in Paris on Thursday ahead of the G7 Summit this weekend.