Wreaths have been laid at the site of one of three bombs which exploded 40 years ago today in the single worst day of atrocities in the Troubles.
Relatives of the dead and survivors of the 1974 Dublin-Monaghan bombings gathered at a special memorial on Talbot Street in the Irish capital.
Among them were Tomassino Magliocco, who now lives in Italy and whose father Antonio died in a bomb on Parnell Street, and Iris Hall, whose father Archie Harper was killed in Monaghan.
Taoiseach Enda Kenny laid a wreath along with the members of the Justice for the Forgotten group which announced on Wednesday it is suing the British Government to get access to classified files they believe will confirm collusion in the bombings.
Thirty-three people were killed, including a pregnant woman, and almost 300 people injured in the no-warning bombs, three in Dublin and one in Monaghan in the space of 90 minutes.
The Ulster Volunteer Force was blamed.
Ireland's Foreign Affairs Minister Eamon Gilmore increased pressure on Prime Minister David Cameron over files on the bombings on the back of the announcement of the lawsuit and called for information to be released.
Margaret Urwin, spokeswoman for Justice for the Forgotten, said she hoped action would follow.
"The Tanaiste issued a strongly worded statement and restored funding for which we are very grateful," she said.
"For a long time we have been asking that the Taoiseach issue a statement, he has called in the parliament on the British to act but I think it's much more significant when they make a statement, and a public statement is significant.
"We hope it will be followed up by action by the British."
Justice for the Forgotten alleges some of the bombers were British agents and that security forces knew about the terror plot in advance.
Northern Ireland Secretary of State Teresa Villiers said she will continue to hold talks with the Irish Government over the bombings.
"The passage of time does not lessen the pain and loss for those who lost loved ones to terrorism during the Troubles," she said.
Ms Villiers said the previous British Government co-operated fully with past inquiries and went to great lengths to provide what information it could. She added: "Since May 2010 both my predecessor and I have discussed this issue several times with counterparts in the Irish Government and I continue to do so."
Author and historian Tim Pat Coogan delivered an oration before a memorial mass was celebrated at the pro-Cathedral in nearby Marlborough Street by Archbishop of Dublin Diarmuid Martin.
In his sermon the Archbishop said great strides towards reconciliation have been made in the 40 years since the bombings.
"But we also know that reconciliation will only be lasting when it is based on truth," he said.
"In a modern human rights culture, which fights against impunity and seeks reconciliation in truth, it is anachronistic that there are still those who place obstacles to the revelation of the truth of what happened in these bombings 40 ago."