BRUSSELS  - The European Union’s chief Brexit negotiator said on Thursday no "decisive progress" had been achieved in the third round of Brexit talks, and that opening talks on the two sides' future ties in October was doubtful at the current pace.

Britain’s Brexit minister David Davis said the sides "made some concrete progress", that there was "high degree of convergence" on the future Irish border and that London would “interrogate rigorously” what it would pay the EU on departure.

Brexit talks have resumed in Brussels more than a year after Britons narrowly voted in a national referendum to leave the EU. Despite both the EU and Britain being on a short deadline to deliver a deal, the talks have seen a slow start.

"Over the course of this week we have made a number of useful clarifications on a number of points, for instance the status of border workers," Michel Barnier told a joint news conference with Davis after the latest round of talks.

"However, we did not get any decisive progress on any of the principle subjects, even though on the discussion we had about Ireland - that discussion was fruitful."

Barnier scolded London for demanding the "impossible" - including having a say on the EU’s single market rules while being outside of it - in a series of position papers the British government released last week.

He said both sides disagreed again on Thursday on the EU's demand, firmly rejected by Britain, that the European Court of Justice must be allowed to police the enforcement of rights of EU citizens residing in Britain after Brexit, and vice versa.