European Commission President Jean-Claude Juncker said it was highly unlikely negotiations on Britain's split from the EU could expand by the end of October to include a future trade relationship as planned.
"We will not have sufficient progress," Juncker said as he arrived for an EU summit in Estonia's capital, Tallinn, on Friday. "I'm saying there will be no sufficient progress from now until October unless miracles will happen."
Britain wants to advance as fast as possible to the next stage of discussions, which would address its future relationship with the bloc, as well as a future trade deal. But the EU has insisted there must first be progress on three key issues: the rights of EU citizens living in Britain and Britons living in Europe, a financial settlement, and the fate of Northern Ireland.
EU leaders are expected to decide if talks can move forward at a summit on October 19-20.
May: 'Very good progress'
In contrast to Juncker's evaluation of Brexit negotiation progress, British Prime Minister Theresa May, who delivered a major Brexit speech in Florence a week ago aiming to re-invigorate deadlocked negotiations, said she was heartened by the "different atmosphere" and "very good progress" at this week's talks.
"I am pleased that the negotiations have been making progress and I look forward to developing that deep and special partnership with the EU," she told reporters in Tallinn.
Specifically, May said negotiators were now closer to agreeing on the rights of expatriate citizens, adding that she was committed to encouraging Europeans to stay in Britain.
"I value the contribution that EU citizens have made in the United Kingdom, but I also want to see the citizens that are living in other European Union countries have their rights guaranteed as well," she said.
May did not, however, say whether she thought there was enough momentum to move talks on to trade relations.
Irish Prime Minister Leo Varadkar also referred to "a better vibe and a better mood coming out of the negotiations" between the EU and Britain. However, he also acknowledged that there was "more work to be done."
"We're not yet at the stage where we can say that sufficient progress has been made to allow us to talk about the new relationship and trade," Varadkar added. "I don't know whether we will be able to make that call until later in the month."
nm/sms (AFP, AP, Reuters, dpa)