European leaders have endorsed a joint negotiating position on Brexit.
The 27 remaining members states formally agreed their talks strategy at a special European Council meeting in Brussels.
Council president Donald Tusk tweeted the outcome of their discussions, saying: "Guidelines adopted unanimously. EU 27 firm and fair political mandate for the Brexit talks is ready."
Speaking as he arrived at the summit earlier, Mr Tusk said: "We need to remain united as the EU 27. It is only then that we will be able to conclude the negotiations, which means that our unity is also in the UK's interest.
"As for now I feel strong support from all the EU institutions, including the European Parliament, as well as all the 27 members states.
"I know this is something unique, but I am confident that it will not change," he added.
With much of the ground work having been done ahead of the summit, leaders took minutes to endorse the joint approach.
The guidelines remained essentially unchanged from the draft proposals published by Mr Tusk last month.
Full text of the draft guidelines can be read here.
Central to that is the "phased" approach, with EU leaders insisting the shape of a future trading relationship can only be considered when progress is made on the terms of the UK's departure.
Mr Tusk said it was vital for the 27 to remain united.
"It is only then that we will be able to conclude the negotiations which means that our unity is also in the UK's interest," he said.
"As for now I feel strong support from all the EU institutions, including the European Parliament, as well as all the 27 member states.
"I know this is something unique, but I am confident that it will not change."
Earlier in the week, German chancellor Angela Merkel said it appeared the UK was under the "illusion" that it could retain EU benefits once it departed the bloc.
Asked if he agreed with Mrs Merkel's analysis, EU Commission president Jean-Claude Juncker told reporters in Brussels: "That's my impression, yes."
Mr Tusk has insisted "sufficient progress" must be made on disentangling the UK from its ties and obligations to the EU before discussions can turn to the post-Brexit relations.
Key issues in the first phase are the size of the disputed "divorce bill" the UK will need to stump up on departure - estimated by EU officials at around £50 billion - and addressing uncertainty over the rights of EU citizens living in the UK and British expats residing on the continent.
Mr Tusk has also signalled a desire to resolve the thorny problem of the Irish border - and how to avoid customs and immigrant checkpoints on the politically sensitive frontier - before moving negotiations to the second stage.
Entering the summit meeting, Irish premier Enda Kenny said his fellow EU leaders were aware of the "difficulties" Ireland faced due to Brexit.
"You are aware that Ireland has prepared assiduously and very well for this over the last 18 months and our priorities are reflected in the document from the European Parliament and from the European Council," he said.
Arriving at the landmark Europa building for the summit, Mr Tusk had said: "We all want a close and strong future relationship with the UK - there is absolutely no question about that.
"But before discussing our future we have to sort out our past, and we will handle it with genuine care, but fairly.
"This I think is the only possible way to move forward.
"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.
"And the Commission has already prepared a precise and detailed list of citizens' rights we want to protect."
Aside from dealing with the present day Irish border, the European Council is set to provisionally agree its approach if the day came when the people of Northern Ireland voted to end partition and join a united Ireland.
While not part of the Brexit negotiating guidelines, a statement to the minutes of Saturday's summit is expected to reflect that, in such circumstances, Northern Ireland would automatically assume the EU membership already held by the Republic of Ireland, rather than having to reapply.
However, those minutes will only be formally adopted at the next EU council meeting next month.
Comparison between draft and final framework
A comparison between the draft EU negotiating guidelines and the final framework adopted at the European Council summit show only a small number of amendments.
In terms of identifying the key issues in phase one of the talks, the guidelines now list securing protections for EU citizens ahead of disentangling the UK from its obligations (i.e. settling the exit bill). In the draft paper it was the other way round.
That may not prove significant, although in his pre-summit comments European Council president Donald Tusk said resolving uncertainty around citizens' rights was the EU and UK's "number one priority".
In regard to the financial settlement, the final guidelines provide more detail on the "obligations and liabilities" the UK will be asked to cover.
It lists issues resulting from the MFF (the EU's long term spending plan) as well as "those related to the European Investment Bank (EIB), the European Development Fund (EDF) and the European Central Bank (ECB)".
The paragraph listing the other areas of potential future co-operation, aside from trade, has added "foreign policy" to security, defence and the fight against terrorism and international crime.
A paragraph has also been inserted stressing that any future UK-EU relationship should "safeguard financial stability in the Union and respect its regulatory and supervisory regime and standards and their application".
In recent weeks debate has flared around whether a free trade deal would include the financial services industry and, if it did, whether City of London institutions would still be bound by Brussels oversight.
The paragraph on the Irish border has made clear the EU's support of the 1998 Good Friday peace agreement relates to "all its parts".
Some structures agreed in what is an international accord between the UK and Republic of Ireland were based on EU law and the UK will now face pressure to ensure post-Brexit laws in Northern Ireland do not undermine the terms of the peace deal.
One of the more controversial elements of Mr Tusk's draft guidelines in March was a suggested veto for Spain on any future UK/EU agreements that involved Gibraltar.
There has been no change to the wording of that paragraph.