British Prime Minister Theresa May accused the other 27 EU countries of lining up to oppose Britain over Brexit after Germany's Angela Merkel said the UK should have no "illusions" over the exit process.
"A third-party state will not have the same rights or even superior rights to a member state," the German chancellor told parliament two days before a key summit in Brussels.
"This may sound self-evident, but I have to say this clearly because some in Britain seem to have illusions on this point," she said. "That would be a waste of time."
May accused the 27 other EU member states of lining up against Britain.
"Our opponents are already seeking to disrupt those negotiations –- at the same time as 27 other European countries line up to oppose us," May told a campaign rally in Leeds, northern England.
"That approach can only mean one thing -– uncertainty and instability, bringing grave risk to our growing economy with higher taxes, fewer jobs, more waste and more debt."
The British leader is currently campaigning after calling a snap election on June 8, hoping to shore up her mandate ahead of two years of gruelling negotiations.
The leaders of the other 27 EU nations have stressed a united stance as they plan to meet Saturday to set down the bloc's "red lines" even though the talks will not begin until June, after Britain's election.
"The negotiations will be very demanding, without a doubt," said Merkel, the leader of the biggest EU economy.
The EU has toughened its strategy, making new demands over financial services, immigration and the bills Britain must settle before ending its 44-year-old membership of the bloc.
Britain could be required to give EU citizens permanent residency after living there for five years, in a challenge for May's Conservative government, which has vowed to limit immigration.
The EU's latest draft negotiating guidelines, agreed on Monday, seek to ensure Britain does not get a better deal outside the bloc than inside.