The 1998 peace deal ended Northern Ireland's decades-long violent conflict known as the Troubles.

Mr Sunak will welcome the US president to Northern Ireland on Tuesday evening.

They will attend events in Belfast to mark 25 years since the agreement.

The prime minister said the agreement was a "powerfully rare example of people doing the previously unthinkable to create a better future" for Northern Ireland.

"It is that promise of a better future that we offered to everyone in Northern Ireland that I will be thinking of first and foremost over the coming days," he said.

"Making good" on that promise was his responsibility as prime minister, he added.

Speaking on Sunday, Taoiseach (Irish Prime Minister) Leo Varadkar said he plans to "intensify" engagement with Mr Sunak over the Windsor Framework and power-sharing in Northern Ireland.

"One thing I've been struck by watching all the documentaries around the history of the Good Friday Agreement was the extent to which the taoiseach and the prime minister had to be in lock-step, and now that we have the agreement on the protocol, I think it's possible to do that.

"Certainly since Brexit, and even before Brexit, that sort of level of cooperation between the two governments, the two governments working hand-in-hand, hasn't been the same.

"And that's largely because we found ourselves in very different positions."

Leo Varadkar will host a bilateral meeting with President Biden at Farmleigh on Thursday

On Wednesday Mr Sunak will address a Queen's University Belfast conference about the Good Friday Agreement and will later host a gala dinner to commemorate the anniversary.

He has also announced that the UK will host a Northern Ireland investment summit in September.

It will connect international investors with Northern Ireland businesses and showcase the "best of what Northern Ireland has to offer", said the government.

What will Biden do in Belfast?

President Biden is due to make a speech at Ulster University's newly-opened Belfast campus on Wednesday.

It is understood that he will leave Northern Ireland that afternoon to travel to the Republic of Ireland.

His visit to Northern Ireland will be shorter than many people had expected when it was first announced last month.

Speaking after a 1916 Easter Rising commemoration in Dublin on Sunday, Sinn Féin president Mary Lou McDonald expressed disappointment that Mr Biden would not be addressing assembly members in Stormont, RTÉ reports.

"The eyes of the world are on Ireland and the north of Ireland in particular and we have a limbo situation," she said.

Ms McDonald added that the president's visit to Northern Ireland is more "low key" than in the Republic of Ireland.

The UK and Irish government have said it should not be seen as a snub.

Northern Ireland Secretary Chris Heaton-Harris said people should "make the most" of the visit and ensure it was a "positive event".

Tánaiste (Irish Deputy Prime Minister) Micheál Martin said it would be a "manifestation of [Mr Biden's] genuine commitment to the people of Northern Ireland".

"There are many countries across the EU that would love a visit from the American president," he added.

Police in Northern Ireland have said their resources will be stretched during the president's visit.

Last week it said it had "very strong intelligence" that dissident republicans were planning attacks in Londonderry to coincide with Easter and Good Friday Agreement events.

More officers are being put on frontline duty for the coming days.

Where will Biden visit in Ireland?

During his three days in the Republic of Ireland, Mr Biden will attend engagements in Dublin, County Louth, and County Mayo.

The White House has said he is expected to address the Oireachtas (Irish parliament) on Thursday.

Taoiseach (Irish Prime Minister) Leo Varadkar said he was delighted that President Biden would be visiting Ireland.

"When we spoke recently in the White House President Biden was clear that in celebrating the Good Friday Agreement we should be looking ahead, not backwards," he said.