EU leaders have agreed to move Brexit talks on to the second phase, says European Council President Donald Tusk.

This means talks can move on to the long-term relationship between the UK and EU, including trade and security.

The first issue to be discussed, as early as next week, will be the terms of a transition period after the UK leaves in March 2019.

European Commission President Jean-Claude Juncker has warned this process will be "significantly harder".

Mr Tusk tweeted the news after a meeting of the other 27 EU leaders in Brussels. He congratulated UK Prime Minister Theresa May on reaching what the BBC's political editor Laura Kuenssberg said was a major moment in the Brexit process.

EU leaders agree to move on to the second phase of #Brexit talks. Congratulations PM @theresa_may

Mrs May has said she wants both sides to approach the next phase of negotiations, which will determine the long-term shape of the UK relations with the EU, with "creativity and ambition".

The EU has published its guidelines for phase two of the negotiations, with discussions on future economic co-operation not likely to begin until March.

The UK reached agreement with the European Commission last week that "sufficient progress" had been made on so-called divorce issues, such as citizens' rights and financial liabilities, to move onto the next phase.

Mr Juncker said on Friday that the EU's initial priority was to "formalise the agreement" that had been reached before moving forward.

Mrs May is set to discuss her vision of the "end-state" for the UK outside the EU at a cabinet meeting on Tuesday, having suffered her first Commons defeat earlier this week.