Shadow chancellor John McDonnell should be "ashamed" of comments suggesting Irish republican terrorists should be honoured, David Cameron has said.
The Prime Minister joined DUP leader Nigel Dodds in condemnation of the remarks, made in 2003.
In an interview on Monday, Mr McDonnell admitted he may not have used the right words but insisted the sentiment behind them was intended to help the Northern Ireland peace process - adding if his remarks had saved a single life, it had been worth it.
Mr Cameron's comments at Prime Minister's Questions sparked the loudest cheer of the session after a subdued first clash with Jeremy Corbyn.
Mr Dodds said: "The plaques at the entrance door to this chamber in memory of Airey Neave, Robert Bradford, Ian Gow, Sir Anthony Berry, serving members of this House murdered by terrorists as they stood up for democracy and the British way of life.
"They are a reminder of the savagery and brutality of terrorism, as are the gravestones and headstones in Northern Ireland and right across this land.
"The Opposition leader has appointed a shadow chancellor who believes terrorists should be honoured for their bravery. Will you join with all of us on all sides of this House in denouncing that sentiment and standing with us on behalf of the innocent victims and for the bravery of our Armed Forces who stood against the terrorists."
Mr Cameron replied: " You have spoken for many, many in this House and I would say many, many, the overwhelming majority of people, the vast majority of people in our country.
"Airey Neave was the first MP I can remember because he was my MP. Ian Gow was one of the first politicians I ever wrote a speech for and there will never be another kinder, more gentle public servant in this House, so cruelly murdered and his family having that life taken away.
"I have a simple view which is the terrorism we faced was wrong, it was unjustifiable, the death and the killing was wrong. It was never justified and people who seek to justify it should be ashamed of themselves."
In 2003, Mr McDonnell told a meeting in London: "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."
Speaking to Channel 4 News on Monday, Mr McDonnell said: "Some of us had to go out there - I might not have chosen the right words - and actually explain to them they could stand down with dignity.
"I know as a result of that I got attacked, but actually it worked. And if it saved one life, it was worth it."
In further remarks to The Guardian, Mr McDonnell said he "abhorred" the loss of civilian life.