EU negotiator Michel Barnier said the bloc's position needed to be "better understood and respected" by the UK if an agreement is to be found.
His UK counterpart David Frost said "significant" disagreement remained on "a number of important issues".
The UK has ruled out extending the December deadline to reach a deal.
The latest round of talks, the first to be held in person since the Covid-19 crisis struck, came after both sides agreed to "intensify" negotiations last month.
Negotiations have continued throughout the pandemic via video link. An additional five weeks of in-person talks are planned for July and early August.
BBC Europe reporter Gavin Lee said the latest round of talks had broken up a day early, with a discussion between the two chief negotiators tomorrow cancelled.
Mr Frost said the face-to-face talks had given "extra depth and flexibility" to discussions on a "full range of issues" over trade and a future partnership.
"But they have also underlined the significant differences that still remain between us on a number of important issues," he added.
"We remain committed to working hard to find an early understanding on the principles underlying an agreement."
Equally, Mr Barnier said "serious divergences remain" after the four days of talks, although the EU believed an agreement was still possible.
'Equivalent engagement'
"The EU engaged constructively, as we had already done during the fourth round of negotiations in June," he added.
"The EU expects, in turn, its positions to be better understood and respected in order to reach an agreement.
"We need an equivalent engagement by the United Kingdom."
Mr Barnier underlined that the EU expects "parallel progress" in all areas of the negotiations.
This is a point of difference with the UK - which wants to negotiate separate agreements in areas such as fisheries, alongside a basic free trade deal.
Mr Barnier also reiterated the EU would not agree to a deal without "robust" guarantees on the so-called "level playing field" for competition between business.
He added this would include the area of state support for companies.
Just like when it was an EU member, the UK remains tied to the bloc's "state aid" rules during the 11-month transition period due to end in December 2020.
The UK has not yet unveiled plans for its post-Brexit state aid regime, but PM
Boris Johnson has previously said he wants to make it easier for the UK government to provide assistance to struggling firms.
The two sides also remain deadlocked over the issue of fishing rights - an area where they had previously pledged to find agreement by last month.
The EU wants to uphold its existing access to British waters for vessels from member states, to avoid economic disruption for their fishermen.
But the UK wants to hold annual talks with the bloc over access to its waters, as it currently does with nations such as Norway.
