Do not ask victims to move on - Irish president
Relatives of people killed or injured during the Troubles should not be expected to "move on" and they "deserve the truth - no more, no less", Ireland's president has said.
Michael D Higgins was speaking on the 50th anniversary of the Dublin and Monaghan bombings, which killed 33 people - one of them was nine months pregnant.
Three bombs were set off in the Irish capital and one in the town of Monaghan.
Loyalist paramilitary group the Ulster Volunteer Force (UVF) admitted carrying out the attacks 19 years later.
However, nobody was ever convicted, and Mr Higgins condemned what he said was a "manifest failure" to investigate the worst bombing in the country's modern history.
He said it was a "matter of profound regret" and "unacceptable" that no one had been held accountable.
Mr Higgins said both the UK and Irish governments had failed to "initiate suitable responses in the aftermath of the attacks".
The president also said there were systemic failures at state level including possible collusion between security forces and loyalist paramilitaries, the disappearance of important forensic evidence and a refusal to supply information.
The bombings resulted in the largest loss of life on any single day of the Troubles.
President Higgins also addressed the UK's controversial Legacy Act and said it was "not morally acceptable, nor is it politically feasible" to ask those affected by the Troubles to forget the past.
"We share, on this island and beyond, a collective responsibility to find a way to deal ethically with the legacy of the Troubles," he added.
"A strategy of feigned amnesia, or hoping time will deliver one is simply not an option, nor is any strategy of continuing the protection of previous evasions or failures to act."
'Denied justice'
"I share with the relatives gathered or represented here their feeling of being abandoned and failed by the system, of their being denied justice for the loss of loved ones," Mr Higgins added.
He said the relatives need more than an empathetic ear, adding: "Justice demands that they deserve the truth - no more, no less."
Taoiseach (Irish Prime Minister) Simon Harris and Tánaiste (Irish Deputy Prime Minister) Micheál Martin also attended the wreath laying-ceremony along with the president.
At the scene, BBC News NI crime and justice correspondent Julian O'Neill
The bell of St Patrick’s Church in Monaghan rang at 6.58pm, the precise moment the bomb exploded fifty years ago.
It tolled for one minute.
The church is beside a memorial sandstone pillar which stands in the centre of the border town, inscribed with the names of the seven people killed in the blast.
The memorial was the venue for an outdoor service attended by around 1,000 people, including the Irish President Michael D. Higgins.
PSNI chief constable Jon Boutcher also attended.
Roads in the town centre were closed during the event.
Wreaths were laid for the victims and a minute’s silence was held.
Sharon Askin, whose father Paddy was killed in the bombing, read out the names of all those murdered in both locations.
Earlier, Mr Martin said the loss and suffering of the Dublin-Monaghan families was "magnified" by an "inadequate investigation" at the time.
He said further inquires raised the question of possible collusion and he had "been following up" with Northern Ireland Secretary Chris Heaton-Harris "on the provision of sensitive material which may help answer some of those questions".
Additionally, the Police Service of Northern Ireland (PSNI) has released all documentation related to the Dublin-Monaghan bombings, its chief constable said.
He added the PSNI was committed to providing "unfettered access" of unredacted material for the investigation of legacy cases.
A Mass took place at St Mary's Pro Cathedral on Friday in memory of the people who were killed and injured in the bombings.
Catherine Doyle and Sandra O'Brien were among the relatives of those killed who attended the events in Dublin.
Ms Doyle's sister Anna and Ms O'Brien's brother John were a married couple.
They were killed along with their children, five-month-old Anne-Marie and 17-month-old Jacqueline.
"Today is very important. Every year is important, it’s not just the 50th year," Ms O'Brien told BBC News NI ahead of the memorial service.