Former Prime Minister Tony Blair has said Brexit has injected tension back into the relationship between Britain and Ireland.
Mr Blair, who was one of the architects of the Good Friday agreement, said the relationship between the two nations needed to be maintained after Brexit.
Speaking at the first cross-party public hearing on Brexit in the European Parliament in Brussels on Wednesday, Mr Blair called the situation "tragic".
He said: "In my view, the reason we managed to achieve the Good Friday Agreement and create the circumstances of peace in Northern Ireland was because the relationship between Britain and Ireland had improved so much.
"And because we're both partners in Europe.
"One of the things that I think is really tragic about the situation is the tension it has injected back into that relationship.
"So, I think so far as we're concerned, we've just got to make it clear to people that this relationship between the Republic and the UK has got to be maintained... and in a way that keeps borders open and therefore secures the basic objectives of the Good Friday Agreement."
His comments come as MPs return to the House of Commons after the Supreme Court ruled Boris Johnson's advice to the Queen on prorogation was unlawful.
The Prime Minister is set to deliver a statement to MPs about the ruling after his crushing defeat.
