The Brexit stalemate looks set to continue after the Irish government said the backstop would not be up for renegotiation at a planned meeting between Boris Johnson and Leo Varadkar.

The two prime ministers will meet early next month but a spokesman for Varadkar said there was no prospect of a rethink on the most contentious part of the withdrawal agreement.

Johnson has been invited by the taoiseach to Dublin with “no preconditions” but the Irish government is keen to avoid any ambiguity.

The meeting will come at a crucial time with MPs who want to avoid a no deal seeking to build a coalition in parliament to block the government from that path.

An Irish government spokesman said: “[The talks] would give both sides an opportunity to gain a better understanding of their respective positions. As has repeatedly been made clear, the withdrawal agreement and the backstop are not up for negotiation.”

The EU has said it will not countenance the ditching of the Irish backstop, an insurance policy that would keep Northern Ireland in the single market and the whole of the UK in a customs union with the bloc to avoid a hard border on the island of Ireland.

Whitehall sources insist that Downing Street wants to strike a deal with Brussels before 31 October despite recent accusations from the EU that Johnson is offering no grounds for fresh talks.

Johnson’s chief EU adviser, David Frost, is expected to visit Brussels again in the coming days. His first visit two weeks ago led EU officials to conclude that the a no-deal Brexit was the new British government’s “central scenario”, a claim denied by Downing Street.

UK sources insist that it is EU intransigence that is heightening the risk of a no-deal Brexit. But the concern at the British government’s position was reflected in a flurry of social media activity by key EU officials in recent days.

The former deputy chief negotiator for the bloc, Sabine Weyand, “liked” a tweet which claimed that “a good faith negotiator, seeking to replace a previously agreed legal text, would at this stage produce a further text setting out with precision the amendments they want”.

Stefaan De Rynck, a lieutenant to the EU’s chief negotiator, Michel Barnier, retweeted claims that British farmers would need to engage in mass culling of livestock in the event of a no-deal Brexit. He wrote: “You may believe this story or not. But clearly, Brexit means an adaptation for UK economy. Brexit disrupts. EU agreed to UK ask for a transition period in withdrawal agreement that eases adaptation. In other words, “inflexible” EU agreed in withdrawal agreement to help mitigate negative impact of Brexit on UK.”

Johnson will meet the European commission president, Jean-Claude Juncker, for the first time at a G7 meeting in Biarritz at the end of this month. In an interview with an Austrian newspaper over the weekend, Juncker said “the British would be the big losers” in a no deal Brexit. “They pretend it’s not like that, but it will be”.