The group voiced their displeasure at reports Merkel warned British PM Boris Johnson in a phone call on Tuesday morning that a Brexit deal was “overwhelmingly unlikely” unless he agreed to Northern Ireland remaining in the EU’s customs union.

Leave.eu responded on Twitter, slamming Merkel for her “reprehensible” demands, claiming such a move only underlined the “true colours of our supposed European allies.” The group attached a meme with a somewhat suggestive picture of the German chancellor and war-like language.

The word Kraut is a derogatory term for a German, particularly a German soldier, commonly used by Britain and its allies during World War I and World War II.

The tweet has provoked anger online with some suggesting such rhetoric was “outrageous, offensive and inciteful.” David Lammy, Labour’s Tottenham pro-remain MP issued an apology to the EU, branding the pro-Brexit group’s tweet as “xenophobic bile.”

Johnson and Merkel discussed the intractable Brexit issue, with the UK PM stressing that if this is the EU’s new established position, then a deal is “essentially impossible not just now but ever,”according to a Number 10 source.

Last week, the UK government unveiled its plans for a renegotiated Brexit deal, with Johnson insisting that they presented a “very reasonable offer.” Under the new proposals it would see the Irish backstop replaced with electronic and a “number of physical” customs checks on the island of Ireland.

Brussels gave a damning response to the plans, claiming they could not even serve as a rough outline for a final agreement. Johnson has been rushing to strike a deal ahead of the October 31 deadline for leaving the bloc.