(Bloomberg) -- Talks between Britain and the European Union over their future trading relationship failed to make much progress on Saturday, and the two sides appear no closer to a breakthrough with three weeks to go before the final deadline.

Negotiations will continue overnight and into Sunday, but the current status remains “very difficult,” a U.K. government official said. Prime Minister Boris Johnson and European Commission President Ursula von der Leyen are set to speak again later Sunday, after which they’re expected to come to a firm decision on the future of the negotiations.

“The prime minister will leave no stone unturned in this process, but he is absolutely clear: any agreement must be fair and respect the fundamental position that the U.K. will be a sovereign nation,” the government official said.

One of the key hurdles to any deal, according to Johnson, is the bloc’s demand that the U.K. follow future changes in the EU’s rules and regulations. Without an agreement, Britain will have to do business with its neighbor on World Trade Organization terms from Jan. 1, which would result in higher costs for companies and disrupt long-established supply chains.

“As things stand, the offer on the table from the EU remains unacceptable,” the official said.

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