A no-deal Brexit will result in a border on Ireland and checks on goods crossing between Europe and the UK, EU Commission President Jean-Claude Juncker confirmed.
Mr Juncker insisted that Brussels was "in no way responsible" for the consequences of a no-deal scenario, saying the blame would lay squarely with the UK.
He also hit back angrily at claims from Brexiteers that his an unelected bureaucrat, calling that a "typical British lie".
In an interview on Sky News' Ridge on Sunday programme, Mr Juncker said "we can have a deal" if alternative arrangements called for by Boris Johnson's government provided the basis for replacing the controversial Irish border backstop.
The Prime Minister has demanded that the backstop - a contingency plan to prevent a hard border by keeping the UK aligned with many of Brussels' rules - should be scrapped.
Mr Juncker said: "We have to make sure that there will be no hard and physical border between the two parts of the Irish island and things have to be done on a level playing field.
"If these three objectives are met by the alternative arrangements, then we don't need the backstop. The backstop was never an instrument having been put in place for whatever will happen.
"No, it was put in place in order to preserve the rights of the internal market and of the island of Ireland."
But in the event of a no-deal Brexit, Mr Juncker said there would have to be checks. He added: "I'm not an architect of new border stations. The British have to tell us exactly the architectural nature of this border.
"I don't like a border because after the Good Friday Agreement, and this Good Friday Agreement has to be respected in all its parts, the situation in Ireland has improved. We should not play with this."
He said: "We have to make sure that the interests of the European Union and of the internal market will be preserved.
"An animal entering Northern Ireland without border control can enter without any kind of control the European Union via the southern part of the Irish island. This will not happen. We have to preserve the health and the safety of our citizens."
Mr Juncker suggested that some Brexiteer MPs are "forgetting about the history" of Northern Ireland and Ireland.
He said the decision by the Luxembourg Prime Minister Xavier Bettel to speak to the media next to an empty podium after Mr Johnson pulled out of a joint appearance due to noisy protests was "not very helpful".
Mr Juncker also criticised former UK prime minister David Cameron over the build-up to the 2016 Brexit referendum, claiming he failed to explain the agreement reached with Brussels.
"We agreed the deal back in 2016, I think, between David and ourselves but this deal was never explained to the British public. Never."