The European Council has responded to the UK's notification of its intention to leave the EU.
A downbeat Tusk said: "There is nothing to win in this process. In essence this is about damage control."
Tusk said: "Both I and the Commission have a strong mandate to protect the interests of the 27."
He added: "Brexit has made us, the community of 27, more determined and more united than before."
Here is the statement in full:
Today, the European Council received a letter from the British Prime Minister, Theresa May, notifying the United Kingdom's intention to leave the European Union. This notification follows the referendum of 23 June 2016 and starts the withdrawal process under Article 50 of the Treaty. We regret that the United Kingdom will leave the European Union, but we are ready for the process that we now will have to follow.
For the European Union, the first step will now be the adoption of guidelines for the negotiations by the European Council. These guidelines will set out the overall positions and principles in light of which the Union, represented by the European Commission, will negotiate with the United Kingdom.
In these negotiations the Union will act as one and preserve its interests. Our first priority will be to minimise the uncertainty caused by the decision of the United Kingdom for our citizens, businesses and Member States. Therefore, we will start by focusing on all key arrangements for an orderly withdrawal.
We will approach these talks constructively and strive to find an agreement. In the future, we hope to have the United Kingdom as a close partner.
President Tusk has convened the European Council on 29 April 2017.