Northern Ireland’s police have warned of the risk of terror attacks on their officers as US president Joe Biden and UK prime minister Rishi Sunak prepare to visit Belfast to mark the 25th anniversary of the region’s landmark peace deal.

Biden and Sunak are expected to celebrate the Good Friday Agreement, which was signed on 10 April 1998 and ended Northern Ireland’s conflict by establishing a power sharing government involving the region’s unionist and nationalist communities.

The visits, which come after the UK intelligence agency MI5 last week increased the security threat for Northern Ireland to “severe”, coincide with more than 90 notified unionist parades and other unscheduled events, according to police.

A key focus is the city of Londonderry, also known as Derry, where dissident republican groups are expected to hold a rally on Monday to commemorate Ireland’s 1916 Easter rising.

“We have a real concern that there’s the potential for public disorder,” Bobby Singleton, assistant chief constable of the Police Service of Northern Ireland, told the BBC.

He added: “Experience tells us that can often become a platform for an attack on our officers.”

Simon Byrne, chief constable, said 300 extra officers, including firearms and search specialists, had been drafted in from around the UK for what would be a £7mn policing operation surrounding the events to mark the 25th anniversary of the Good Friday deal.

He told Northern Ireland’s independent supervisory policing board on Thursday: “We’re . . . assuming that attempts will be made to draw us into situations that may likely cause disorder over the next few days.”

In February, in the most serious incident in years, the dissident republican group the New IRA shot and seriously injured detective chief inspector John Caldwell at point blank range. The incident happened outside a youth club in Omagh, County Tyrone, in front of Caldwell’s son and other children.

Mark Durkan, a Good Friday Agreement negotiator who served as deputy first minister in Northern Ireland’s government for the Social Democratic and Labour party, said dissident republican groups who never abandoned the armed struggle for a united Ireland “might well feel the need or the temptation to do something for the optics”.

He added that with the world’s media focused on the region, there could be “pathetic” attempts by such groups to flex their muscles, including bomb scares and hoax devices, “because they know that will pick up publicity”.

Biden is expected to inaugurate an Ulster University campus in Belfast on Wednesday and to meet political and business leaders before visiting the Republic of Ireland.

He will not address the Northern Ireland assembly at Stormont, which has been mothballed for nearly a year after a boycott by the Democratic Unionist Party over post-Brexit trading arrangements.

DUP leader Sir Jeffrey Donaldson dismissed suggestions that the heightened terror threat was related to the local political limbo.

“While Stormont was sitting for many years these dissident republicans engaged in violence, they murdered police officers,” he told the BBC.