Donald Trump raised the prospect of Irish reunification during closed-door talks with the country’s leaders, The Telegraph can reveal.

The US president broached the issue of a united Ireland in his private meetings with Micheál Martin, Ireland’s taoiseach, and Catherine Connolly, the Irish president, a US official said.

These conversations took place before he made the extraordinary intervention in one of Britain’s most sensitive topics by announcing at a press conference that he would “love” to see Northern Ireland and the Republic unified.

Hours after Mr Trump’s comments, The Telegraph revealed that the leaders of Scotland, Wales and Northern Ireland will gather on Monday to sign a deal designed to kick-start the break-up of the United Kingdom.

On Sunday, Mr Trump doubled down on his position, saying: “I’ve always loved the people of Ireland, and it just seems to me that you have Northern Ireland and you have Ireland, and it would seem to me that one of the naturals of all time is putting them together.

“So that’s only my opinion. And by the way, many people agree.”

Asked if the UK should hold a referendum on unification, Mr Trump said that while many think such an event won’t happen, “these things happen”.

‘He’s a very nice guy, but on the liberal side’

Mr Trump said he would “say nothing” about Scottish independence, stating he will “save that for another day”.

On Andy Burnham, the new Prime Minister, Mr Trump said: “I’ve spoken to him. I think he’s a very nice guy. He tends to be on the liberal side, unfortunately.”

Gerry Adams, the former leader of Sinn Féin, welcomed Mr Trump’s intervention and said it represented the sentiment of the United States as a whole.

He accused Mr Martin of putting himself “outside” the supporters of reunification.

“They reflect the broad North American sentiment towards Irish unity and particularly the Irish diaspora towards Irish reunification.

“Micheál Martin has put himself outside this positive attitude to Irish Unity in Ireland and the diaspora. He needs to correct this and play a leading part in this process.”

Under the terms of the agreement, the UK’s Northern Ireland secretary can decide to hold a border poll, and has a duty to call one if it appears likely a majority would vote for Irish unification.

The people of the Republic of Ireland must also vote in favour to affect constitutional change.

On Sunday, Angela Rayner brushed off Mr Trump’s backing for a united Ireland, saying the Government remains committed to the Good Friday Agreement.

She told Sky News’s Sunday Morning programme: “Donald Trump is Donald Trump, and the president will say and speak his mind as he sees it.”

Ms Rayner added the Government was “really serious” about the Good Friday Agreement and would “continue on that path”.

Tom Tugendhat, the shadow foreign secretary, told the BBC’s Sunday With Laura Kuenssberg programme that Mr Trump’s remarks had been “unhelpful” and accused him of “playing games”.

Mr Tugendhat added: “I suppose I knew he was a Republican, I didn’t know he was that kind of a republican.”

“This sort of loose talk about the future of democratic countries is deeply unhelpful and creates unnecessary tension.”

Robert Jenrick, Reform UK’s economic spokesman, told the BBC that Mr Trump “shouldn’t have weighed into British politics”.

On Monday, the leaders of Scotland, Wales and Northern Ireland will gather to put pen to paper on a joint declaration demanding the right to hold independence referendums.

The unprecedented meeting builds on the momentum of Mr Trump’s comments, and after Mr Burnham suggested to MPs that he would authorise another Scottish referendum if there were a “clear consensus” in favour of one.

Mr Trump, wearing a navy suit and white USA hat, shook the hand of golfer Shane Lowry, the tournament leader, and stood off to the side with his son, Eric Trump.

Before Mr Trump arrived, Eric Trump greeted Mr Martin and his wife and gestured toward the shoreline, saying, “it doesn’t get much better than that”.