Former IRA commander Martin McGuinness said "his heart goes out" to protestors at a peace lecture he is to give in a town bombed by the terror group.
Mr McGuinness, now the Northern Ireland Deputy First Minister, was invited to speak tonight in Warrington by Colin Parry, who lost his 12-year-old son in the bombing of the town in 1993.
Mr Parry, who has since set up a peace foundation in the name of his son, said while he has not forgiven the IRA for the bombing, history was "littered" with terrorists who had now become peace-makers.
A small band of around 12 demonstrators stood outside the venue protesting at Mr McGuinness' speech later at the Tim Parry - Johnathan Ball Foundation for Peace.
Earlier Julie Hambleton, whose sister Maxine, 18, was killed in the Birmingham pub bombings, compared Mr McGuinness' giving a talk on peace to "asking Myra Hindley to give a talk on child protection."
Mr McGuinness said he "understood" the objections and described the path to peace as a "journey."
"My heart goes out to them because they too are people that have suffered as a result of the conflict in the north of Ireland," he said.
"I fully appreciate that there are other people who don't feel able to make that journey. I would be the last to criticise them.
"My heart goes out to all the victims of the conflict.
"I feel very compassionate to all of them.
"We need to be sorry for everything that happened with the people involved in the conflict."
Asked specifically about the Warrington bombing, he added: "It's absolutely shameful that two young boys lost their lives."
Colin Parry said the peace foundation had an "open door" policy with their founding principle that all opinions from opposing sides of conflicts welcome in the pursuit of peace.
"I would hope that the people outside, rather than criticise us for that, would recognise that's a different path but an honourable path," he said.
Tim Parry and Johnathan Ball, aged three, were killed when bombs planted in litter bins in the town's main shopping area were detonated shortly after midday on a sunny Saturday afternoon.
No warning was given and no one has been prosecuted for the outrage on March 20 1993, that left 56 people injured.
Johnathan was in the town with his babysitter to buy a card for Mother's Day, the next day, when he was killed.
The death of the two boys sparked a public outcry in the UK and on both sides of the border in Ireland.
Mr Parry and Tim's mother, Wendy Parry, have set up the Tim Parry Johnathan Ball Foundation for Peace, which has since become an internationally recognised centre for conflict resolution and victim support.
Outside the venue, one of the protesters against Mr McGuinness' speech was Brian Hambleton, 58, who dropped his sister Maxine off at the Birmingham pub blasted by IRA bombs on the evening of November 21, 1974.
Mr Hambleton, from Birmingham, said: "It makes me feel ill being within 100 yards of him.
"I'm here for a reason and that reason is that man's murky, violent past.
"He has to be answerable for his past before he goes forward with peace.
"He shouldn't be speaking in there, he should be on his knees begging people's forgiveness.
"This town lost two beautiful young boys like I lost my sister. How Mr Parry can greet him and invite him here is beyond me. It is immoral."
In his speech Mr McGuinness spoke about his own and Ulster's journey to peace and his hopes for the future.
"I was once in the IRA. I am now a peace builder," he said.
"It has been a journey which has involved much hurt and pain.
"I have followed many coffins and stood beside many grieving families in the years since.
"But there can be no greater tragedy in life than parents having to bury their child.
"No child, whether they were killed with a plastic bullet fired by a British soldier or RUC man, or killed by an IRA action or by a loyalist gang should have died.
"I remember well the tragedy; the scenes of overwhelming grief on the streets of Warrington were heart-rending.
"As a republican leader it would be hypocritical for me to seek to distance myself from the consequences of armed struggle or the IRA's role in it.
"Nor can or would I attempt to excuse the human loss caused by the IRA bomb in Warrington.
"Regrettably the past cannot be changed or undone. Neither can the suffering, the hurt or the violence of the conflict be disowned by Republicans or any other party to the conflict."
Mr McGuinness said the challenge is to ensure that there can never be a repeat of what went before.
"Dealing with the past will help and guide us in our building of the future. And building for the future will enable us to deal with the past.
"Compromise is not a dirty word."