Senior EU figures are expected to react later to Theresa May's combative speech in which she accused some in Brussels of "not wanting Britain to prosper".
Launching the Conservative Party's general election campaign after the dissolution of Parliament, she suggested leaks and threats had been "deliberately timed to affect the result of the general election".
Two senior sources within the European Council refused to comment directly on the accusations when asked by Sky News, but MEPs gave their reaction on Wednesday evening.
Mairead McGuinness, vice president of the European Parliament, warned of the damage such "emotive, electioneering language" could do to the subsequent negotiations.
"The election that's happening in the UK will of course impact the current discussions in the UK, and probably here as well, but when all of this is over there will have to be a settling down and dealing with reality," she said.
Conservative MEP Daniel Hannan told Sky News that the Prime Minister was right to fire back after European Commission president Jean Claude Juncker said it was a "constructive meeting" then leaked a different account to a German newspaper.
After being "traduced in a foreign newspaper with the most grotesque version of events, I think she has every right to feel cross about it", he said.
Back in Britain, Labour branded Mrs May's move as "foolish", the Liberal Democrats said it was "desperate and bizarre" while the pressure group Leave Means Leave welcomed the "robust position".
On Thursday Mr Juncker will be holding a news conference in the afternoon and the European Parliament's negotiator Guy Verhofstadt will also appear before the cameras.
It is likely both men will be asked for their reaction to Theresa May's remarks.