The EU's long-serving Brexit negotiator Michel Barnier has urged all sides to shoulder their responsibilities to Northern Ireland and what he described as a "very fragile" peace process.
Speaking to the European Parliament, Mr Barnier also warned that Brexit had been a "failure" of the European Union that politicians and EU institutions had to learn from.
Mr Barnier was speaking ahead of a plenary vote to ratify the Trade and Cooperation Agreement (TCA) which sets out the future relationship between the EU and UK post-Brexit.
He told MEPs: "For Ireland, peace is very important. Everybody has to shoulder their responsibilities...and respect what they have signed up to. This is something that affects peace and lasting trust between the EU, the UK, Ireland, all of us.
"Ireland, we don't look at it just in terms of goods, services and trade. Instead, men and women who need peace, which is very fragile."
Mr Barnier recalled four years of "very difficult negotiations" and said that as well as a difficult divorce, Brexit was a "warning".
"It's a warning Brexit. And it's a failure, a failure of the European Union. And we have to learn lessons from it as politicians here in the European Parliament and Council, in the Commission, in all of the capitals.
"Why did 52% of the British vote against Europe? There are reasons for that social anger and tension which existed in many regions in the UK, but also in many regions of the EU," he said.
"Our duty is to listen and understand the feelings of the people and the feelings of the people, this social anger shouldn't be confused with populism, and we should do everything to respond to that in each of the member states and at the union level and continue to show the value added of what we do together to ensure that we can be prosperous, independent, safe and secure," he added.
Earlier the President of the European Commission said the EU would work closely with the UK to find constructive solutions to issues around the Northern Ireland Protocol.
Ursula von der Leyen told MEPs: "In recent days and weeks, we have seen a new constructive dynamic and we will continue to work closely with the UK to find constructive solutions that respect what was agreed.
"The next step is to mutually agree on a compliance path with concrete deadlines and milestones and to support this process. [European Commission] Vice President [Maros] Sefcovic will continue to engage with all stakeholders in Northern Ireland to listen to their concerns and to see what needs to be done."
She added: "We need solutions, not sound bites, if we are to make the protocol work for the benefit of everyone in Northern Ireland. This is the commitment and responsibility we all took when we agreed to the protocol. And the European Union is steadfast in its determination to make it work."
President von der Leyen recalled a report adopted by the European Parliament at the height of the hunger strikes which, she said, paved the way for a more direct role for the EU in the Northern Ireland peace process.
The so-called Martin Report, she said, had focused on housing, social and regional policy.
"But thanks to the leadership of John Hume in particular, it ensured for the first time that the question of peace and prosperity of Northern Ireland was seen as an explicit issue for the European Union.
"This was the beginning of an enduring commitment of this house to the people of Ireland and Northern Ireland. And as John Hume himself used to say, there are no easy answers, no quick fix solutions."