The remaining 27 EU countries adopted Brexit negotiating guidelines in a show of unity ahead of talks with Britain, European Council President Donald Tusk said on Saturday.

"Guidelines adopted unanimously. EU27 firm and fair political mandate for the #Brexit talks is ready," Tusk tweeted as leaders met in Brussels.

The guidelines call for a "phased approach," noting that progress must first be made on the issues of citizens' rights and a financial settlement before negotiations on a possible post-Brexit trade agreement can begin.

"We are ready," said the EU's chief Brexit negotiator, Michel Barnier. "We are together."

The joint announcement came as the 27 EU nations met in Brussels without British Prime Minister Theresa May, one month after she triggered two years of exit talks on March 29.

'Unity in action'

European Commission President Jean-Claude Juncker hailed the summit's agreement, noting in a tweet that it took under 15 minutes for leaders to approve. He said it showed "unity in action."

Tusk earlier noted that leaders "need to remain united as the EU 27" but that EU unity is also in Britain's interest since it could boost chances for a swift Brexit deal.

German Chancellor Angela Merkel echoed those comments, saying that although the bloc wants to have "good relations" with Britain, "we as 27 also want to represent our interests. That has succeeded extremely well so far."

The final bill

Juncker said that while the bloc had not presented Britain with a precise bill for its financial obligations to the bloc, "cautious estimates" put the figure at up to 60 billion euros ($65.4 billion.)

"We would like first ... to hold negotiations over the terms of Britain's divorce," Merkel said. "Of course, financial issues are some of the questions about the divorce."

"We want to have good relations with Britain in the future, but we as 27 also want to represent our interests," the German chancellor added.

French President Francois Hollande said while the bloc did not want to punish Britain, the UK would be weaker once it was outside the bloc.

"It must not be punitive, but at the same time, it is clear that Europe must defend its interests and that the United Kingdom will have a weaker position tomorrow outside of Europe than it has today inside Europe,"

According the wording of the guidelines "A single financial settlement - including issues resulting from the MFF (Multiannual financial framework - the EU's 7-year budget which ends in 2020) as well as those related to the European Investment Bank (EIB), the European Development Fund (EDF) and the European Central Bank (ECB) - should ensure that the Union and the United Kingdom both respect the obligations resulting from the whole period of the UK membership in the Union. The settlement should cover all commitments as well as liabilities, including contingent liabilities."

Some of the EU leaders were already discussing how to deal with British negotiation tactics. Belgian Prime Minister Charles Michel warned that London may try to divide the bloc to its advantage.

"Maybe the British government will do its utmost to split the 27 nations and it is a trap we need to avoid," Michel said.

Drawing clear lines

Tusk said the first priority will be to ensure the rights of EU and British citizens living on each other's side who will be immediately impacted by the split. Around 3 million citizens from the remaining EU 27 nations live in the UK while up to 2 million Britons live on the continent.

"We need real guarantees for our people to live, work and study in the UK and the same goes for the Brits," Tusk added.

Although the EU guidelines say that trade talks cannot begin without "sufficient progress" on the divorce issues, leaders were still discussing how to define such progress.

Juncker told reporters on Saturday that Britain had blocked billions of euros in EU spending last week. British officials said they were unable to approve a package of 6 billion euros in spending measures: "We sought to delay a vote on a sensitive file in keeping with our pre-election protocol," a British official said.

Juncker and EU officials were unimpressed and the EC President commented "It would be desirable and it would facilitate the beginning of the negotiations if the UK were to be able to withdraw the reserve it has entered."

Divorce talks with the British government are expected to begin after the UK holds snap elections on June 8, but the EU is due to give an official mandate to Barnier on May 22.

rs,jm/sms (AP, AFP, dpa, Reuters)