EU officials have warned that real progress was needed before the summit starting on Wednesday.
The British Government said there were still "unresolved issues" but it remained committed to making progress at the summit.
An EU official said no further negotiations were planned before the leaders of EU countries convene in Brussels. Both sides previously agreed that a special November meeting would be the deadline for reaching an agreement since Britain is set to leave the EU on March 29.
The EU and the UK are seeking an elusive compromise position on the difficult Irish border question ahead of the summit. The "Irish backstop" is the main hurdle to a deal that spells out the terms of Britain's departure from the EU and future relationship with the bloc.
After Brexit, the currently invisible frontier between Northern Ireland and Ireland will be the UK's only land border with an EU nation. Britain and the EU agree there must be no customs checks or other infrastructure on the border, but do not agree on how that can be accomplished.
Raab, Britain's Brexit secretary, was not expected in Brussels, but he made a last minute trip for an in-person meeting with Barnier.
"With several big issues still to resolve, including the Northern Ireland backstop, it was jointly agreed that face-to-face talks were necessary," Raab's office said.
The EU's "backstop" solution — to keep Northern Ireland in a customs union with the bloc — has been rejected by Britain because it would require checks between Northern Ireland and the rest of the UK.
The alternative — to keep the entire UK in a customs union until a permanent solution can be found — has outraged pro-Brexit members of May's Government, who claim that approach would limit the country's ability to strike new trade deals around the world.
The idea is also anathema to the Democratic Unionist Party, a Northern Ireland Protestant party that props up May's minority government.
So even if May strikes a deal with Brussels, she will struggle to get it past her government and Parliament at home.
Raab's predecessor, David Davis, wrote in the Sunday Times that May's plans for some continued ties with the EU even after Britain leaves the bloc is "completely unacceptable" and must be stopped by her ministers.
May is struggling to build a consensus behind her Brexit plans ahead of a Cabinet meeting tomorrow night that will be followed by the EU summit. If Davis' call for a rebellion is effective, the Cabinet meeting is likely to be fractious.
Davis and former Foreign Secretary Boris Johnson resigned from May's Cabinet this year to protest against her Brexit blueprint. The two men have become vocal opponents of May's plan, saying it would betray the Brexit vote and leave Britain in a weakened position.
DUP leader Arlene Foster remains opposed to any Brexit plan that would require checks on goods travelling between Northern Ireland and Britain, as some EU leaders have suggested as part of a backstop.
May's Brexit plan has also been questioned by some senior figures in the Labour Party, further dimming the Prime Minister's hopes of winning parliamentary backing for any Brexit deal she reaches with EU officials.
- AP
