Joe Biden will hold a bilateral meeting with Rishi Sunak today after arriving in Northern Ireland last night to mark the 25th anniversary of the Good Friday Agreement.
The two leaders met briefly before the president drove away in an armoured car amid a scattering of snow.
Mr Biden and Mr Sunak’s meeting will come before the US president meets the leaders of Northern Ireland’s five main political parties.
However, the White House said there will not be a formal group meeting with the leaders.
The Stormont powersharing assembly, which was established in the Good Friday Agreement peace deal in 1998, is not currently operating due to a protest over post-Brexit trading arrangements by the DUP, the largest unionist party in Northern Ireland.
Following his meeting with party leaders, Mr Biden will deliver an address at Ulster University’s new £350m Belfast campus where his remarks will commemorate the Good Friday Agreement.
The peace deal largely ended 30 years of bloodshed between republicans and loyalists.
Mr Sunak will not attend Mr Biden’s keynote speech, with Downing Street on Tuesday denying that the engagement between the pair would be “low-key”.
Speaking to reporters before his departure, Mr Biden said that his top priority was to “make sure the Irish accords and the Windsor Agreement stay in place, keep the peace”.
His son Hunter Biden and sister Valerie Biden Owen are believed to be accompanying him for the trip.
A major security operation will be in place for Mr Biden’s Northern Ireland visit at an estimated cost of £7m.
Around 300 officers from other parts of the UK will travel to the area to help police a series of events to mark the anniversary.
Mr Biden will travel across the border to Ireland later today where he will tour Carlingford Castle in County Louth, an area to which he has traced his ancestral roots.
Then it’s off to Dublin, where he is expected to visit Irish President Michael D Higgins on Thursday.
Mr Biden will take part in a tree-planting ceremony and ringing of the Peace Bell at the president’s official residence, Aras an Uachtarain.
Following that ceremony, he will meet the Irish Prime Minister Leo Varadkar and address the Irish parliament.
A banquet dinner at Dublin Castle will follow on Thursday evening.
The president’s trip will end with a visit to County Mayo on Friday, where he has connected with distant cousins.
A descendant of Irish immigrants to the United States, Mr Biden will deliver remarks at St Muredach’s Cathedral in Ballina, County Mayo, to which his great-great-great-grandfather Edward Blewitt sold 27,000 bricks in 1827.
The bricks were used to build the cathedral and their sale helped to fund Mr Blewitt’s passage to the US with his family in 1851.
The president’s trip comes at an uncertain time for Northern Ireland, where power sharing in Stormont is still on hold and the terror threat has been raised to severe – meaning an attack is highly likely.
Mr Biden’s arrival came hours after four suspected pipe bombs were found by police in a cemetery in Northern Ireland.
Officers sealed off the City Cemetery in Creggan, Derry/Londonderry, on Tuesday following the discovery of a suspicious device.
There were some disturbances on Easter Monday when petrol bombs were thrown at an armoured police Land Rover in Creggan during what police described as an “unnotified” march by dissident republicans.