Former US president Bill Clinton is expected in Northern Ireland to mark the 20th anniversary of the Good Friday Agreement.

A conference will feature key players involved in the deal including ex prime ministers Tony Blair and Bertie Ahern.

Former US Senator George Mitchell, who chaired the talks, will be among the guests in Belfast.

The agreement helped bring an end to 30 years of sectarian conflict, known as the Troubles.

It was ratified in a referendum on both sides of the Irish border in May 1998 and set up a power-sharing assembly to govern Northern Ireland by cross-community consent.

However, the deal proved difficult to implement and was amended by the St Andrew's Agreement in 2006.

The Northern Ireland Executive has not met since January 2017 due to a bitter dispute between the DUP and Sinn Féin.

"The lesson with these things... is that once you've got a viable peace process you've got to just work at it and work at it and realise that the right comparison is with what things were like during the course of the Troubles," Mr Blair told the BBC's Today programme.

"We used to wake every day to death and destruction."

'Trimble bullied'

The DUP's Sir Jeffrey Donaldson, who was part of the Ulster Unionist negotiating team in the run-up to the agreement, said the party's then leader David Trimble was bullied into signing a flawed deal.

"It didn't see an end to paramilitarism, it didn't see the promised political stability that the agreement heralded and here we are 20 years on from the agreement without a government," he said.

"Northern Ireland is in a better place today than it was 20 years ago, that's for sure, but we still have a long way to go and the flaws in the agreement that were not addressed at the time still need to be addressed."

Sinn Féin's Máirtín Ó Muilleoir said the promise of the agreement has not been fulfilled.

"The spirit endures... the letter of the Good Friday Agreement endures... the principles of the Good Friday Agreement will guide us," he said.

"It was founded on this awkward but marvellous architecture of rights and of inter-relationships and interconnections and I think we have to return to that and this issue of rights."

To mark the agreement's anniversary, a conference is being held at Queen's University in Belfast, featuring key protagonists including Mr Clinton.

Prof James McElnay, the university's acting vice-chancellor, said: "His role and influence on the peace process in Northern Ireland was pivotal to ensuring all parties reached agreement in April 1998.

"To have him back Northern Ireland for this significant anniversary is a privilege."

Others attending include Jonathan Powell, who was an adviser to then Mr Blair at the time of the peace agreement, Lord Trimble and Seamus Mallon - the former first and deputy first leaders of the Northern Ireland Assembly.

Later, Mr Clinton and Mr Mitchell will both receive the freedom of Belfast in a special ceremony at the Ulster Hall.

They will be the 83rd and 84th recipients of the freedom of the city of Belfast.