Shadow chancellor John McDonnell has been criticised for trying to "excuse" his call for IRA terrorists to be honoured after he apologised for the "offence" he had caused.
The Labour MP admitted for the first time that it had been a "mistake" to say in 2003 that "the bombs and bullets" of republicans had been responsible for bringing about the peace process.
But he also argued that the intervention had been "worth doing" as it helped keep the peace process on track.
David Cameron condemned the comments as a source of "shame" when they were raised during PMQs this week - the first session featuring Jeremy Corbyn as opposition leader.
Mr McDonnell told a meeting in London 12 years ago: "It's about time we started honouring those people involved in the armed struggle. It was the bombs and bullets and sacrifice made by the likes of (hunger striker) Bobby Sands that brought Britain to the negotiating table.
"The peace we have now is due to the action of the IRA."
Appearing on BBC1's Question Time last night, Mr McDonnell said: "I accept it was a mistake to use those words, but actually if it contributed towards saving one life, or preventing someone else being maimed, it was worth doing because we did hold onto the peace process.
"There was a real risk of the republican movement splitting, and some continuing with the armed process. If I gave offence, and I clearly have, from the bottom of my heart I apologise."
Mr McDonnell, who had also described the presence of British troops in Northern Ireland as an "occupation", said he had to talk to republicans on their terms.
Stressing that he "rejected political violence", the shadow chancellor added: "I had to use the language that republicans understood so we could secure the path to peace.
"There were risks, but it was worth taking because now people are not dying on the streets of Northern Ireland."
DUP MP Jeffrey Donaldson said Mr McDonnell had to make clear that there could be no justification for violence in a democracy.
He told BBC Radio 4's Today programme: "I have to accept his apology, but I would say that what he then sought to do was to excuse it or explain it away and frankly I don't buy the notion that what he said was designed to encourage republicans to stick with the peace process.
"I think, what he said when he said, he not only failed to recognise the hurt that his remarks would cause but I think that he was being at the very least ambivalent on the question of political violence in a democratic society, and for me that is the issue he needs to be more clear on.
"Once you cross the line and once you even suggest there is some justification for that kind of violence - for exploding bombs outside shops or blowing hotels up or attacking hospitals and murdering men, women and children in the name of a political cause when you have a democratic avenue that you can choose and you can take - then you are in very dangerous territory."
Peace campaigner Colin Parry, whose son Tim was killed aged 12 by an IRA bomb in Warrington in 1993, questioned whether Mr McDonnell was "sincere".
He told Today that he appeared to be changing his position because of a public backlash.
"I'm afraid that is the way I think. To use the words he did so explicitly back then, they don't sound like chance remarks in the hope that he was assisting the peace process," he said.
"He must have been under enormous pressure ... Obviously the past does come back to haunt you when your political position changes and you become high profile."
Mr McDonnell also used his Question Time appearance to apologise for an "appalling joke" in 2010 about wanting to assassinate Margaret Thatcher.
He said: "It was an appalling joke. It's ended my career in stand-up, let's put it that way, and I apologise for it as well."
The shadow chancellor said Labour favoured a return to the "reasonable" 50p top rate of income tax, playing down suggestions that he and Mr Corbyn could push for it to rise to as much as 70p.
He also insisted that Labour was not advocating withdrawal from the Nato alliance.
Mr McDonnell said he had spoken to his party leader about the row following Mr Corbyn's decision not to sing the national anthem at a Battle of Britain memorial service.
"I said afterwards 'why didn't you sing?' and he said 'actually I normally do', but it was quite a moving event and he was casting his mind back to the war," Mr McDonnell said.
"The national anthem isn't just for those who are monarchists, it's for everyone and it represents the whole country and that's why people sing it."
Meanwhile, Mr Corbyn has given his clearest indication yet that Labour will campaign in favour of continued European Union membership in the in/out referendum promised by David Cameron by the end of 2017.
Writing in the Financial Times, the new Labour leader - who had been criticised for appearing to leave the door open for backing withdrawal - said: "Labour is clear that we should remain in the EU. But we too want to see reform."
While the party opposes reforms being sought by Mr Cameron that would reduce workers' rights, the shadow cabinet was in agreement that the answer was "not to leave the EU but to pledge to reverse those changes with a Labour government elected in 2020", Mr Corbyn said.
His comments came as Mr Cameron told business leaders that Labour would get "nowhere near power" under Corbyn's leadership.