Britain has responded to Barnier's statement, with its Brexit minister David Davis saying he was surprised to hear that the EU's negotiator was unclear on Britain's demands in any transition period.
"We are seeking a time-limited period that maintains access to each other's markets on existing terms," Davis added.
Earlier in the day, Michel Barnier stated that the sides disagreed on several issues, including citizens’ rights and the application of European rules during the transition and if these disagreements persist, "the transition is not a given."
The EU negotiator stressed that "the UK must accept all the rules and the conditions right until the end of the transition, and must also accept the inescapable consequences of its decision to leave the European Union."
On Wednesday, the EU published a draft agreement which presupposes that Brussels will be able to slap sanctions on Britain, including freezing its single market access, if London fails to stick to the transition period-related deals.
In December, the sides finished the first phase of negotiations. The second phase of the talks, which the sides are engaged in now, is dedicated to the transition period in EU-UK relations after Brexit, and their future long-term trade and security cooperation.
Brexit negotiations between the United Kingdom and the European Union started in June 2017, a year after Britain held the Brexit referendum and UK Prime Minister Theresa May officially invoked Article 50 of the Lisbon Treaty, launching the country's EU withdrawal process. The talks are due to be completed by the end of March 2019.