European Union leaders on Saturday unanimously agreed to "tough" negotiating guidelines for Brexit talks, suggesting that they will demand Britain agree on payments to the bloc before considering a new trade deal.

EU Council President Donald Tusk said on Twitter: "Guidelines adopted unanimously. EU27 firm and fair political mandate for the Brexit talks is ready."

The 27 EU leaders took less 15 minutes to approve the draft guidelines for the negotiations, which were issued on March 31 by Tusk, the Guardian reported.

Talks with Britain will begin after the general election on June 8.

The EU is expected to demand that Britain resolves the key divorce issues of citizens' rights, the divorce bill and the Irish border before any talks on a future trade deal between the UK and the EU can begin.

"We all want a close and strong future relationship with Britain. There's absolutely no question about it. But before discussing the future, we have to sort out our past. We will handle it with genuine care, but firmly," Tusk said before the meeting. 

"We also need solid guarantees for all citizens and their families who will be affected by Brexit, on both sides. This must be the number one priority for the EU and the UK," he said.

The first of the key issues of the EU guidelines is that Britain must resolve the fate of three million EU citizens living in Britain and one million Britons on the continent, and what happens to their rights to work and claim benefits abroad.

The EU-27 will also call for action to avoid a "hard border" between the Republic of Ireland and Northern Ireland, as fears persist that Brexit could undermine the peace process, the daily reported.

The most contentious issue of the EU guidelines, however, is likely to be Britain's exit bill, estimated at around $65 billion, covering financial commitments made by the bloc during Britain's time as a member.

Asked what sufficient progress would mean in relation to the UK's divorce bill, a senior EU diplomat said the European council's guidelines were quite explicit about what would be expected and that there would be little "wiggle room".

Meanwhile, French President Francois Hollande said there would inevitably be "a price and a cost for the UK — it's the choice that was made".

"We must not be punitive, but at the same time it's clear that Europe knows how to defend its interests, and that Britain the UK will have a less good position tomorrow outside the EU than today in the EU," he said.