US House Speaker Nancy Pelosi has said no trade deal between Britain and the United States which undermines the Good Friday Agreement is possible.
In a forceful address to a special joint sitting of the Houses of the Oireachtas, Mrs Pelosi emphasised the depth of support in Washington DC to the Northern Ireland peace process.
She said "we treasure the Good Friday Accord" as a "beacon to the world".
"On that holy day the world saw the dawn of peace in Northern Ireland that few had dared to dream,” she said in paying tribute to the efforts of political leaders here.
In relation to Brexit, Speaker Pelosi said:
She restated comments made earlier this week that a trade agreement between the UK and the US post-Brexit would not happen if it damaged to the Belfast Agreement.
"Let me be clear if the Brexit deal undermines the Good Friday Accord, there will be no chance of a US-UK trade agreement," she said.
"I say that hopefully that we would not have to face that reality," she said.
"As you face the challenges posed by Brexit, know that the United States Congress, Democrats and Republicans in the house and in the Senate, stand with you," she said.
During her 30-minute address, Mrs Pelosi also expressed her support for Ireland's bid for a seat on the UN Security Council.
Mrs Pelosi pointed out in her speech that both Ireland and the US "know the joy of independence" and both "endured the traumatic experience of civil war and the satisfaction of rebuilding our nations".
"It is these mutual experiences that our nations affirm for each other and to the world our democratic values and commitment to freedom. When Ireland proudly proclaimed its independence our people stood together,” she said.
She also paid tribute to the considerable contribution of the Irish in the US, recalling that the Irish served in the Lincoln army to "perserve the Union and save our nation".
She also praised U2 lead-singer Bono, who was in the distinguished visitors' gallery, for his music and advocacy work, saying he represented the best of the Irish. The singer rose and took a bow when applauded by elected members, many of whom afterwards queued to shake his hand.
Bono was spotted talking to former Taoiseach Enda Kenny and veteran senator Terry Leyden ahead of Mrs Pelosi's address.
Mrs Pelosi was invited to speak in Leinster House by Ceann Comhairle Seán Ó Fearghail.
The Speaker told the Dáil that she is deeply honoured by her welcome to Ireland, "a beautiful and magical land".
At the start of her address, Mrs Pelosi references the 1963 visit of President John F Kennedy, and quoted his comments to the Dáil that while Ireland and the US were divided by distance, they were united in history.