British former prime minister Tony Blair on Thursday urged pro-UK unionists in Northern Ireland to emulate their 1998 predecessors and show leadership to unlock present-day paralysis.

Blair was reflecting on the upcoming 25th anniversary of the Belfast/Good Friday Agreement, which ended three decades of bloody unrest under his premiership.

In a veiled attack on former UK premier Boris Johnson, he warned against "grandstanding" by leaders in London, and welcomed a breakthrough deal by Prime Minister Rishi Sunak to regulate trade in Northern Ireland.

"The difference between this peace process and many others around the world is that we had the benefit, at that time, of leaders who were prepared to lead," Blair told a House of Commons committee.

"And each of them had to say things to their own followers that were uncomfortable, that people didn't like," he said.

But today, the hardline Democratic Unionist Party (DUP) is refusing to enter a power-sharing government with the pro-Irish Sinn Fein party.

The DUP says it is still studying whether Sunak's deal with the European Union, dubbed the Windsor Framework, meets its tests to resume government in Belfast.

Blair said Brexit was always going to produce "a difficult circle to square" with regard to Northern Ireland, which under the 1998 agreement cannot have physical border checks with EU member Ireland.

"And my reason for supporting what the government, this prime minister, has done on the Windsor agreement is that I think it represents the most practical way forward that minimises all the theoretical objections."

Under the Good Friday Agreement of April 10, 1998, pro-Irish militants agreed to lay down their arms and pro-UK unionists agreed to share power in Belfast.

Brexit has strained the uneasy contract. And last month, a senior police officer was shot and seriously wounded in front of his son after coaching a youth football team.

Police suspect a dissident nationalist paramilitary group called the New IRA was to blame.

"Whatever the problems in Northern Ireland, what people should never forget, it's a world better from where it was," Blair stressed.

"And if we exercise common sense and realism today, we can keep the peace intact, and ensure there is a situation where whatever difficulties and challenges that there are in Northern Ireland can be resolved by negotiation and agreement, not violence."