The Minister for Foreign Affairs has said that Ireland will not approve of any deal on Brexit unless it guarantees the full protection of the Good Friday Agreement and the peace process.

Simon Coveney said it is clear that Ireland is being prioritised in the negotiations, which began today.

Mr Coveney said he intends to build on the resolution of such complex issues when he meets the European Union's chief Brexit negotiator, Michel Barnier, in Luxembourg tomorrow.

Mr Barnier 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.

Mr 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 British 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.

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'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 issues surrounding the border between Northern Ireland and the Republic, he said, as well as the issue of the rights of EU citizens in the UK and Britons living in other EU countries and the "single financial settlement" of outstanding liabilities.

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 €100 billion.

Mr Barnier and Mr Davis will meet every four weeks over the coming months, bringing their teams together for a matter of days each time.

Different working groups will negotiate on the issues of the border, expat rights and the financial settlement.

Mr Davis said talks over the border had taken more time than anything else, with discussions on the "political sensitivities" of the issue and the "determination to maintain as near as possible an invisible border".

Answering questions, the Brexit Secretary defended the decision to make the issue the subject of a dialogue rather than a working group.

"This is a technically difficult issue, but it's one which I am certain is soluble or that will probably take us until the end of the process when we have already decided what our customs and free trade arrangements are," he said.

"But that's why we're starting now and that's why this needs to be dealt with by dialogue of the two highest ranking people, the two coordinators in this team.

"There's no doubt in my mind that this is right at the top of the priorities we need to resolve in this negotiation."

Mr Davis also denied suggestions the agreed timetable showed Britain's "weakness" and insisted it is "completely consistent" with the Government's aim of parallel trade and exit talks.

"It's not when it starts it's how it finishes that matters," he said.

"The UK has been crystal clear in our approach to the negotiations, the withdrawal process cannot be concluded without the future relationship also being taken into account.

"They should be agreed alongside each other, this is completely consistent with the Council's guidelines which state nothing is agreed until everything is agreed."