"We want EU citizens in Britain to have the same rights as British citizens who live in the EU," Barnier told a news conference in Brussels, noting that the British position at the moment does not guarantee these equal rights, Reuters reported.
Barnier said that the European Court of Justice should be the "ultimate guarantor" of these rights, and if Britain opposed this "it would create uncertainty." Britain wants to regulate citizens' rights under British law.
He said there should be progress on all three priority Brexit issues before talks can begin on trade issues.
"These three priority subjects for the first phase of negotiations are inseparable. In other words, progress on one or two of these topics will not be sufficient to move on to discussions about our future relationship with the United Kingdom."