Negotiations over a Brexit deal descended into further chaos Tuesday, with a UK government source telling the BBC that a deal was “essentially impossible” after a call between Boris Johnson and Angela Merkel went south over the question of Northern Ireland.

The UK prime minister and German chancellor had spoken earlier in the day about proposals Johnson made to the European Union, but the source said she made clear that a deal based on his pitch was “overwhelmingly unlikely.”

Johnson’s office then blamed the EU for a breakdown in negotiations, sparking a warning from a top EU leader against playing a “stupid blame game.”

Johnson’s office gave a gloomy assessment after the call.

Ten Downing Street said in a statement that Merkel had told the prime minister that the deal was likely doomed unless Northern Ireland remained in a customs union with the EU — something the UK insists can’t happen.

The PM’s office said that “if this represents a new established position, then it means a deal is essentially impossible not just now but ever.”

The EU denied its position had changed.

The Republic of Ireland remains a member of the EU, and the bloc wants to maintain the open borders between Ireland and Northern Ireland established by the Good Friday peace deal in April 1998.

European Commission spokeswoman Mina Andreeva said “the EU position has not changed. We want a deal. We are working for a deal with the UK.”

European Council President Donald Tusk tweeted testily that “what’s at stake is not winning some stupid blame game.”

“At stake is the future of Europe and the UK as well as the security and interests of our people,” he said, addressing Johnson. “You don’t want a deal, you don’t want an extension, you don’t want to revoke, quo vadis?” — a Latin phrase meaning “where are you going?”

Irish Deputy Prime Minister Simon Coveney tweeted that it was “hard to disagree” with Tusk’s statement, saying it reflected “frustration across EU and the enormity of what’s at stake for us all.”

EU leaders have demanded more “realism” from Britain in response to a Brexit plan proposed by Johnson.

The bloc says the proposals don’t fulfill the UK’s commitment to a frictionless border between Northern Ireland and EU member Ireland.

Johnson, meanwhile, has urged the bloc to compromise.

But most of those plans may be halted by an early election. Both the government and the opposition see a national vote as the only way to break Britain’s Brexit deadlock, though they disagree on the timing.

The PM has insisted the UK will leave the EU at the deadline for a deal at the end of the month, with or without a deal.

With AP