The leaders of the US and Britain have reaffirmed their commitment to the Good Friday Agreement as tensions remain around the Northern Irish Protocol.
Joe Biden and Boris Johnson met face-to-face in Cornwall ahead of a G7 summit, with Mr Johnson saying there is "complete common ground" on protecting peace in the North.
The White House denied reports it had rebuked Mr Johnson's handling of the protocol, but a senior White House official said Mr Biden would outline to Mr Johnson that the progress of the Good Friday Agreement "must be protected".
A joint statement from the two leaders after their meeting said they "reaffirm their commitment to working closely with all parties to the Agreement to protect its delicate balance and realise its vision for reconciliation, consent, equality, respect for rights, and parity of esteem".
Following the talks, Mr Johnson said he is "optimistic" the peace process will be kept going. Asked if Mr Biden made his alarm about the situation in Northern Ireland clear, Boris Johnson said: "No, he didn't."
Taoiseach Micheál Martin said Mr Biden's intervention in the situation is welcome and significant "but also from my perspective represents a lot of common sense":
Foreign affairs minister Simon Coveney said it is "no secret" that UK-Ireland relations are strained.
Mr Coveney says Mr Biden's intervention on the Brexit issue "simplifies the message, a deal was agreed for good reason. Now it needs to be implemented."
He said there has been "some strain in the relationship" with the UK because "commitments were made in writing, in terms of how we could protect the island of Ireland as a whole... and so the implementation of that is important."
He also rejected new DUP leader Edwin Poots' assertion that his behaviour was unreasonable during Brexit negotiations saying: "I've been consistent."