European Council chairman Donald Tusk has accused the UK Prime Minister Boris Johnson of trying to "win some stupid blame game" over Brexit.

Tusk was responding after a UK government source told reporters a deal was "essentially impossible" after a phone call between Johnson and German Chancellor Angela Merkel.

The source reported Merkel had said a Brexit deal was "overwhelmingly unlikely" unless Northern Ireland stayed in the European Union's customs union.

The source added that if the call represented "a new established position, then it means a deal is essentially impossible not just now but ever."

"Merkel said that if Germany wanted to leave the EU they could do it no problem, but the UK cannot leave without leaving Northern Ireland behind in a customs union and in full alignment forever," the source said, adding that Merkel told Johnson she thought the EU had a veto on Britain leaving the customs union.

Tusk tweeted to Johnson: "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. You don't want a deal, you don't want an extension, you don't want to revoke, quo vadis?"

Ireland's foreign minister Simon Coveney said Tusk was reflecting "the frustration across the EU and the enormity of what's at stake for us all."

"We remain open to finalize a fair Brexit deal but need a UK government willing to work with the EU to get it done," he added.

The German government declined to comment on the content of the phone call, and an EU spokeswoman said negotiations with the UK continued, with negotiator David Frost expected at the EU Commission on Tuesday.

Merkel's reported comments prompted an angry response from the leader of Northern Ireland's largest party, the Democratic Unionist Party.

Arlene Foster said: "The prime minister's proposals have flushed out Dublin's real intention to trap Northern Ireland in the EU Customs Union forever. We will not accept any such ultimatum or outcome."

Johnson, a leader of the Leave campaign during the UK's 2016 referendum on whether to leave the EU, succeeded Theresa May as prime minister in July with a pledge to get Brexit done on 31 October, with or without a deal.

He said he would rather be "dead in a ditch" than ask for a further extension to the date of the UK leaving the EU.

Last week, he presented fresh plans to the EU, which sought to revamp those drawn up to avoid the need for physical checks being brought back at the Northern Ireland border.

This would have seen the whole UK leaving the EU customs union, but Northern Ireland continuing to apply EU legislation on agricultural and other goods, subject to a vote by Northern Ireland's politicians every four years.

The UK proposal was for any necessary customs checks to take place away from the border.

The comments about the Merkel-Johnson phone call emerged as UK cabinet ministers met in 10 Downing Street.

The UK Parliament opposes the idea of a no-deal Brexit and has passed a law that says Johnson must ask for a delay to Brexit if a deal has not been agreed by 19 October.

The official UK opposition Labour Party's Brexit spokesman Keir Starmer, said: "This is yet another cynical attempt by Number 10 to sabotage the negotiations. Boris Johnson will never take responsibility for his own failure to put forward a credible deal. His strategy from day one has been for a no-deal Brexit."