EU chief negotiator Michel Barnier has called for post-Brexit trade talks to continue beyond the end of the week, despite the UK accusing the EU of taking an "unusual approach" to trade talks.
In a series of tweets, Lord Frost said he was "disappointed" by the conclusions from the summit and "surprised" the bloc is "no longer committed to working 'intensively' to reach a future partnership".
He said the EU was expecting "all future moves" toward a deal to come from the UK, which he called an "unusual approach to conducting a negotiation".
He added the prime minister would set out his "approach" to the future of the talks on Friday.
EU chief negotiator Michel Barnier said fresh "intensive" talks should aim to reach a deal around the end of October.
The prime minister has previously raised the prospect of walking away from negotiations by setting this week's Brussels gathering as a deadline for agreeing a deal.
Boris Johnson said that if by 15 October there was a lack of agreement with the EU on post-Brexit trade, then both sides should “accept that and move on”
Both sides are calling on each other to compromise on key issues, including fishing and limits on government subsidies to businesses.
Another issue more important to many members is the level playing field: the EU wants to ensure neither side can undercut standards or use big subsidies to gain a market advantage. Then there is how any deal would be enforced.
Over the summer, both the UK and EU seemed to agree the end of October was the final date to get a deal done - allowing enough time for it to be ratified before 31 December.
The leaders agreed that the 27 member states and EU institutions should "step up their work on preparedness and readiness at all levels and for all outcomes", but come 7 September, Boris Johnson decided to shorten the deadline.
The leaders invited the European Commission to "give timely consideration to unilateral and time-limited contingency measures that are in the EU's interest" due to the prospect of a no-deal outcome.
European Council President Charles Michel, said: "We are united and determined to reach an agreement but not at any cost," he added.
Michel Barnier, the EU's chief negotiator, echoed that stance and told the news conference that differences still remained between the two sides on key issues.
Mr Barnier also held out the prospect of a two-week extension to Mr Johnson's 15 October deadline, by adding that his team would travel for London for talks next week and would host negotiations in Brussels the week after.
Formal talks began in March and continued throughout the pandemic, initially via video link before in-person discussions resumed over the summer.
If a deal is not done, the UK will trade with the EU according to the default rules set by the World Trade Organisation.
On Thursday, Ireland's foreign affairs minister, Simon Coveney, said he believed "a deal can be done" but admitted the UK and EU remained "miles apart" on the issue of fisheries.
Coveney said that there is still a lot of difficult work to do and believes it is going to take weeks rather than days to finalise a deal.