MARTIN McGuinness has been challenged by unionists over what they described as his "cherry-picking" of the Saville Report.
The inquiry concluded that the deputy first minister was "probably armed" with a machine gun, but it was unable to ascertain whether he fired it.
Outside the Tower Museum Centre yesterday a reporter asked Mr McGuinness: "Did you have a gun any point that day?"
Standing beside what the Press Association described as "a clearly irritated Sinn Fein president Gerry Adams", Mr McGuinness replied: "No."
The Ulster Unionist leader Sir Reg Empey said: "I would say to him: own up Martin because if he's saying that what is in the Saville Report is inaccurate about him the same could be said about what it says about any of the soldiers.
"What he is doing is actually undermining the report. The prime minister was unequivocal in his statement about what happened that day. Martin will have to account for his own actions."
Sir Reg's UUP colleague Tom Elliot said: "Within less than two hours of the publication of the Saville Report, McGuinness has said that there is no truth to the claim that he was armed with a machine gun on that day."
The UUP justice spokesman added: "When pressed by journalists at a press conference to come clean about his activities on Bloody Sunday, he denied that the conclusion set out in the report was true.
"So it has come to this already. McGuinness is only prepared to believe parts of the Saville Report. This selectivity does not serve the community or the truth."
The report said of Mr McGuinness: "...he was probably armed with a Thompson submachine gun, and though it is possible that he fired the weapon, there is insufficient evidence to make any finding on this, save that we are sure that he did not engage in any activity that provided any of the soldiers with any justification for opening fire."
East Londonderry MP Gregory Campbell said if there were to be prosecutions following the report, Mr McGuinness "would have to be first in line".
The DUP man added: "We need to ask Mr McGuinness to get his facts straight here - there needs to be consensus.
"What we know is that he was involved in the IRA leadership in Derry at a time when many people were killed - so I would suggest that if the soldiers who opened fire on Bloody Sunday are to face charges - they need to follow in behind Mr McGuinness who would have to be first in line."
Meanwhile, the ex-Parachute Regiment soldier who wrote at length about Bloody Sunday in yesterday's News Letter expressed surprise at Lord Saville's complete confidence that Mr McGuinness did not engage in activity that provided the soldiers with justification for opening fire.
"Mr McGuinness in his evidence can't fully account for his movements that day," said the former soldier, who wants to remain anonymous for security reasons.
He added: "Lord Saville says it is possible that Martin McGuinness fired the weapon. I still hold to the belief that Martin McGuinness could not have failed to engage, he couldn't have stayed aloof from what was happening.
"He could not have maintained his credibility if he had not engaged and if he had not shown leadership."