The European Union dismissed many of the U.K.’s plans for their post-Brexit relationship as little short of “fantasy” as the mood of negotiations deteriorated and progress stalled.

Three days of talks in Brussels wrapped up with little headway on the most important issues, in particular on how to prevent a hard Irish border, according to an EU official. The EU said the U.K. has still not come to grips with all the steps needed to avoid frontier checks on the island of Ireland, which is a condition for the entire Brexit deal, and hasn’t formally pitched its plan, the official told reporters in Brussels on condition of anonymity.

The EU’s response is a blow to Prime Minister Theresa May who was hoping that, after going some way to bridging divides in her cabinet over the U.K.’s future customs relationship with the EU, the bloc would accept her proposals. But the EU is “confused” by the plan, the official said.

A U.K. official said Thursday that the government doesn’t agree with the EU’s version of the state of the negotiations. A second official dismissed as “laughable” the notion that Britain isn’t providing enough detail, pointing to seven position papers on difficult issues advanced by U.K. officials this week. If the EU persists in insulting the U.K., it risks ending up with a post-Brexit relationship that lets down millions of European and British citizens, the official said.

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Five weeks from a crucial summit when the EU wants “substantive progress” on the Irish issue to allow talks to focus on the future, the two sides have completely different ideas over how to solve the problem on how to keep the border invisible.

The EU says the Brexit treaty must include a “backstop” for Northern Ireland that will last until the border issue is settled as part of the wider U.K.-EU relationship. The EU’s plan is to keep Northern Ireland in the customs union and parts of the single market. May has said no British prime minister would accept such an arrangement.

Speaking late Thursday before the Portuguese parliament’s European Affairs Committee, Michel Barnier, the EU’s chief Brexit negotiator, held fast on the issue while acknowledging it to be an “extremely unique’’ problem.

The U.K. has signaled that it wants to solve the problem by keeping the whole of the U.K. aligned to EU customs arrangements until a future system is ready. But that too is a “fantasy” and won’t work because it ignores the need for alignment of regulations across the border, the EU official said. The official said the U.K. had promised to bring a clearer plan to the next round of negotiations in two weeks’ time.

On matters related to the future U.K.-EU relationship, British negotiators have failed to convince the EU that it accepts the consequences of Brexit, the EU official said. In areas including data exchange, science cooperation, security, defense and the bloc’s satellite navigation project, Galileo, the EU isn’t convinced the U.K. accepts that withdrawal from the bloc means it can’t participate in the way it could as a member.

A U.K. document published Thursday indicated the government was ready to demand repayment if it was forced out of the Galileo project. While that wasn’t brought up in the negotiations, the EU would refuse to talk if it felt it was being “threatened,” the official said.