Update 4.51pm: The EU will take an "Ireland first" stance when it comes to dealing with the border issue in Brexit talks the president of the European Council has said.
Visiting Dublin this afternoon, Donald Tusk said British prime minister will have to come up with a viable solution to the border and protecting the Good Friday Agreement.
"As long as the UK doesn't present such a solution it is very difficult to imagine substantive progress in Brexit negotiations," he said.
He said the EU is a family of nations and "in times of trouble families come together and stand with each other".
"For the EU 27, this is especially the truth when we talk about Brexit."
He said the most difficult issue of the UK's departure in 2019 had been addressed in December.
"Any backsliding on the commitments made so far would create a risk to further progress in Brexit negotiations," said Mr Tusk.
Update 4.07pm: Taoiseach Leo Varadkar has said the EU will enter into Brexit negotiations with an open and constructive outlook.
At a joint appearance in Dublin with European Council president Donald Tusk, Mr Varadkar said:
Mr Varadkar thanked the EU for its support for Ireland's position regarding Brexit issues like the Northern Irish border.
Responding to British Chancellor Philip Hammond's call on Wednesday for a bespoke free trade agreement (FTA) including financial services, Mr Tusk said: "In the FTA we can offer trade in goods with the aim of covering all sectors, subject to zero tariffs and no quantitative restrictions.
"But services are not about tariffs. Services are about common rules, common supervision and common enforcement, to ensure a level playing field, to ensure the integrity of the single market and ultimately also to ensure financial stability.
"This is why we cannot offer the same in services as we can offer in goods. It's also why FTAs don't have detailed rules for financial services.
Responding to Mr Hammond's assertion that it was in the interest of both Britain and EU to ensure that UK-based financial services companies had easy access to the single market, Mr Tusk said: "I fully respect the Chancellor's competence in defining what is in the UK's interest. He must allow us to define what is in the EU's interest."
Mr Varadkar said that his preference was "to avoid a hard border through a wider future relationship between the United Kingdom of Great Britain and Northern Ireland and the European Union".
He said: "We are committed to playing our part in exploring this option or alternative specific solutions in a way that respects the structure of these negotiations.
"That will of course require further detailed progress to be put forward by the UK Government.