The European Union's chief Brexit negotiator has set out tough conditions for Britain to meet during the first months of talks before both sides can start looking at a future relationship.
"The British position does not allow those persons concerned to continue to live their lives as they do today," Michael Barnier said on Tuesday.
Barnier added Britain needs to make sufficient progress on all initial issues before talks can move to the next stage.
"We want EU citizens in Britain to have the same rights as British citizens who live in the EU," he told a news conference in Brussels.
He further said that there were many differences with Britain including citizens' rights that need to be sorted out before talks on a trade deal could start.
Barnier emphasized that was essential that the UK recognize its financial obligations.
"If Britain did not recognize it had some financial obligations, there would be no basis to discuss other issues," he said.
The UK and the EU started the formal Brexit talks last month. UK Prime Minister Theresa May expects the Brexit process to be completed by March 2019 but the EU has warned that the two sides should reach a deal before October 2018.
"I am not hearing any whistling, just the clock ticking," Barnier said referring to the deadline of March 2019 drawing ever closer.
May has made it clear that if the two sides miss the deadline without achieving a deal she would take the country out of the EU regardless, raising the prospects of a so-called “hard Brexit.”
The issue of citizens’ rights is one of the three priorities in the Brexit talks. Nearly three million Europeans are currently living in Britain and around one million Britons living elsewhere in the EU.