US President Joe Biden has landed in Belfast to meet Rishi Sunak to mark the 25th anniversary of the Good Friday Agreement.
The policing operation around Mr Biden’s visit on Tuesday will be the biggest in nearly a decade, at an estimated cost around £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.
Live: Joe Biden lands in Northern Ireland for historic visit
And asked what his top priority was for the trip as he was about to board Air Force One, the president said: “Make sure the Irish accords and the Windsor agreement stay in place; keep the peace. That’s the main thing.”
After his trip to Belfast, Mr Biden will then travel to Ireland from 12 April to 14 April, where he is expected to visit Dublin, Co Mayo and Co Louth.
The visit 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.
There were some disturbances on Easter Monday when petrol bombs were thrown at an armoured police Land Rover in Creggan, Londonderry, during what police described as an “unnotified” march by dissident republicans.
Police in Northern Ireland condemned the incident as “senseless and reckless” and said its officers will review footage of the incident as part of an investigation into potential terrorism offences.
US president to travel to Northern Ireland today: Joe Biden visit – latest
It came as the world marked the 25th anniversary of the Good Friday Agreement, also known as the Belfast Agreement, which has been credited with bringing peace to the region after decades of sectarian conflict.
It is also the day that dissident republicans traditionally mark the anniversary of the Easter Rising rebellion against British rule in 1916.
Elsewhere, Mr Sunak yesterday issued a renewed call to get Stormont back up and running after a year of stalemate, saying: “We must get on with the business of governance”.
His meeting with Mr Biden comes just weeks after his Windsor Framework passed through parliament.
UK and EU officials have since signed off on the new Brexit deal, despite opposition from the Democratic Unionist Party (DUP), which is preventing the return of the Northern Ireland Assembly.
It was the DUP’s objection to the previous Northern Ireland Protocol, which the Windsor Framework replaces, that resulted in Stormont’s collapse.