BRUSSELS (AP) — Talks between the European Union and the United Kingdom on their post-Brexit relationship ground to a near-standstill Friday, with each side accusing the other of blocking progress on a trade deal just weeks before a crucial summit.

The EU's chief negotiator, Michel Barnier, told a news conference in Brussels that a week-long round of talks had been "disappointing, very disappointing."

Barnier said there was no progress on all the most difficult issues and insisted Britain would have to show more realism.

"I am not optimistic in the face of British incomprehension," he said.

The British side echoed the glum assessment, calling the mood of the talks "tetchy."

U.K. negotiator David Frost said the talks had "made very little progress towards agreement on the most significant outstanding issues." In a statement, Frost accused the EU of insisting on "an ideological approach which makes it more difficult to reach a mutually beneficial agreement."

The two sides remain at odds over a range of key issues including fishing and the role of high courts in settling future disputes.

EU leaders and U.K. Prime Minister Boris Johnson are scheduled to have a summit at the end of June, likely by video, to take stock of the talks' progress.

Britain officially left the 27-nation bloc on Jan. 31, but remains within the EU's economic and regulatory orbit until the end of the year. The two sides have until then to work out a new relationship covering trade, security and a host of other issues — or face a chaotic split that would be economically disruptive for both sides, but especially for the U.K.

The U.K.-EU divorce agreement allows for the deadline to be extended by two years, but Johnson's government insists it won't lengthen the transition period beyond Dec. 31.

Most trade deals take years to negotiate, so finishing something as fundamental as this in 11 months would be a Herculean task at the best of times. Many politicians, experts and diplomats believe it is impossible during a coronavirus pandemic that has focused governments' resources on preserving public health and averting economic collapse.

Both Barnier and Frost fell sick with COVID-19, though both have recovered.

While the two men say they have a good personal relationship, the two sides accuse the other of seeking the impossible.

Britain wants a a "Canada-style" free-trade deal that would involve the elimination of tariffs and quotas on most, if not all, goods, along with agreements on services and a range of other issues. The EU says Britain can't have that without signing up to a swath of the bloc's regulations on environmental standards, workers' rights and state aid. Otherwise, they say, there wouldn't be a level playing field.

"We will not trade off our European values for the benefit of the British economy. Our economic and commercial fair play is not for sale," Barnier said.

But the U.K. government says that signing up to EU rules and standards amounts to an unacceptable undermining of the country's independence.

Frost said that to make progress, "we very much need a change in EU approach" for the next round of talks, due to start June 1.

If no deal on their future relationship is agreed by the end of the year, a cliff-edge economic departure would loom again for Britain, with uncertainly over customs rules, airline slots, financial regulation and other standards.

Both sides are already facing a serious recession because of the pandemic and a chaotic split on Dec. 31 wouldn't help.

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Jill Lawless reported from London.