European Council president Donald Tusk has warned that Brexit talks risk becoming "impossible" with a plea for calm amidst a furious war of words between between Westminster and Brussels.
Yesterday Prime Minister Theresa May said EU officials and politicians were seeking to intervene in the June vote, hitting out at "threats" that had been issued against Britain.
And separately, European Commission president Jean-Claude Juncker's chief of staff Martin Selmayr warned that Brexit "will never become a success"
Responding to the comments, Tusk said that the talks are "difficult enough as they are".
"If we start arguing before they even begin, they will become impossible.
"The stakes are too high to let our emotions get out of hand. Because at stake are the daily lives and interests of millions of people on both sides of the Channel," Tusk said.
"We must keep in mind that in order to succeed, today we need discretion, moderation, mutual respect and a maximum of good will."
A spokesman for the European Commission declined to respond to May's comments, but said the EU is not "naive".
"We know there is an election taking place in the United Kingdom, people get excited whenever we have elections. This election in the United Kingdom is mainly about Brexit, but we, here, in Brussels, we are rather busy with our policy work. We have too much to do on our plate," he said.
It comes after details of a private dinner between May, Juncker and EU chief negotiator Michel Barnier were leaked to a German newspaper last weekend.
The leaks included quotes attributed to Juncker stating he was "10 times more sceptical" than before.