The European Union's chief Brexit negotiator has promised to deal with negotiations on the UK's withdrawal in a "constructive" way and said he believed a "fair" deal was possible for both sides and "far better" than the prospect of the UK leaving without an agreement.
Michel Barnier was speaking at the end of the first day of negotiations in Brussels with Brexit Secretary David Davis, who said he was "optimistic" of reaching a good deal.
Mr Davis said Prime Minister Theresa May would brief fellow EU leaders at a summit on Thursday on the UK's approach to the rights of expatriate citizens, which will be set out in detail in a paper on Monday.
Mr Barnier made clear the talks, beginning a year after the UK's Brexit referendum, would take place according to a timetable set by the EU, under which progress on the terms of withdrawal must be made before any discussions on a future trading relationship.
Speaking alongside Mr Davis at a Brussels press conference, he said: "For both the European Union and the United Kingdom, a fair deal is possible and far better than no deal.
"That is what I said to David today.
"That's why we will work all the time with the UK and never against the UK. There will be no hostility on my side.
"I will display a constructive attitude firmly based on the interests and support of the 27."
The first stage of negotiations will cover the issue of the rights of EU citizens in the UK and Britons living in other EU countries, as well as the "single financial settlement" of outstanding liabilities and issues surrounding the border between Northern Ireland and the Republic, he said.
Mr Barnier did not put a figure on the settlement likely to be required from the UK, estimated by some in Brussels at as much as €100bn.
But he made clear that only when the other 27 member states are satisfied that sufficient progress is being made on this issue that the talks can move on to the future trade relationship.
He said: "We have to commit ourselves now mutually to guarantee rights to citizens on either side of the Channel so they can continue their lives as in the past.
"We have to clear the accounts and we have to honour our mutual financial commitments.
"We also have to find solutions to maintaining all the commitments of the Good Friday Agreement.
"It is by lifting uncertainties around these issues that we will lay the foundation and create the climate of trust which will enable us to build a new partnership."