BRUSSELS (AFP) - European Union President Donald Tusk said Britain must first settle the key divorce issues of "people, money and Ireland" before any talks on a post-Brexit trade deal.
In a letter to leaders of the remaining 27 EU countries ahead of a summit on Saturday (April 29), Tusk said that "before discussing our future, we must first sort out our past."
Former Polish premier Tusk said the "only possible approach" was phased talks in which Britain must make "sufficient progress" on the divorce issues before talks on future relations.
Britain had wanted to discuss its divorce settlement with the bloc and a trade deal at the same time.
The EU says the key issues are the fate of three million EU citizens living in Britain and one million Britons residing in the EU; Britain's exit bill estimated at around 60 billion euros; and the fate of the border between Ireland and the British province of Northern Ireland.
"This is not only a matter of tactics, but - given the limited time frame we have to conclude the talks - it is the only possible approach," Tusk wrote to the leaders.
"I would like us to unite around this key principle during the upcoming summit, so that it is clear that progress on people, money and Ireland must come first," he wrote.
"And we have to be ready to defend this logic during the upcoming negotiations."
His comments come a day after a war of words between British Prime Minister Theresa May and German Chancellor Angela Merkel over the two years of negotiations ahead of Britain's exit from the EU in March 2019.
Merkel said Britain should not have "illusions" about getting favourable treatment, but May hit back by accusing the EU 27 of planning to "line up to oppose us."
At Saturday's summit, the EU 27 leaders are set to adopt guidelines for the negotiations on Brexit, following May's formal triggering of the two-year divorce process last month.
They will also discuss whether to back automatic membership for Northern Ireland after Brexit if it ever reunifies with Ireland, an EU Council source told AFP.
Ireland is expected to ask the 27 EU leaders to endorse that idea.
Britons voted to leave the EU in a closely-fought referendum in June 2016.