Jean-Claude Juncker has warned there will have to be controls at the border in Ireland in the event of a no-deal Brexit.
In an outspoken interview, the European Commission president said the UK would be to blame for any fallout for a chaotic exit for the bloc as the EU “did not invent the Brexit”.
Mr Juncker said he wanted to reach an agreement with the UK but the EU had to protect the safety of its citizens.
The Irish border issue has been a major stumbling block in the Brexit negotiations, as Boris Johnson 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.
The senior Brussels official also sought to blame the UK for any fallout caused by a no-deal Brexit, amid frustration in EU circles over perceived attempts from the UK government to shift responsibility away from London.
He said: “The EU is in no way responsible for any kind of consequences entailed by the Brexit.
“That’s a British decision, a sovereign decision that we are respecting but don’t try… not you but to charge the European Union with the responsibility.
“The European Union is not leaving the United Kingdom, the United Kingdom is leaving the European Union.”
Asked who is responsible, he said: “The United Kingdom. Because we did not invent the Brexit.
“We were never pleading in favour of any kind of Brexit. That’s a British decision and so it has to be dealt with in that way.”
His comments came after a meeting with the prime minister in Luxembourg last week, when the country’s prime minister Xavier Bettel left an empty podium for Mr Johnson at a press conference.
Mr Juncker said: “I don’t know if this is helpful. I rather consider that this was not very helpful but it’s his decision.”
Mr Juncker said: “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… Sometimes I have to question that some people are forgetting about the history.”