As a long-awaited report into the shootings of 13 civilians by British troops on Jan. 30, 1972, was published, the prime minister said the first shot was fired by the British army, none of the victims were armed and that the soldiers had given no warning before opening fire.
"There is no doubt .. what happened on Bloody Sunday was both unjustified and unjustifiable. It was wrong," he told the House of Commons in London, adding: "On behalf of the government .... I am deeply sorry."
Publication of the report was greeted with cheers in Londonderry, Northern Ireland's second city, where relatives of those who died joined thousands waiting to see the contents of the 5,000-page report.
Bloody Sunday was one of the most traumatic events in Northern Ireland's 30-year "Troubles," fueling suspicion of the authorities among the Catholic minority and prompting dozens to join the IRA's violent campaign against British rule.
An original 1972 investigation exonerated the paratroopers who shot marchers at a civil rights demonstration in Londonderry, the province's second city.
Thirteen people, all unarmed Catholics, were killed when the soldiers opened fire in the staunchly nationalist Bogside area of the city. A 14th victim later died from wounds. The troops said they shot at people armed with guns or nail bombs.
More than 3,500 people died during The Troubles, which were largely ended by a 1998 peace deal, but emotions still run high in Northern Ireland over its violent history, which pitched Catholics against Protestants.
The inquiry, which took 12 years to report at a cost of more than 190 million pounds ($275 million, 230 million euros), aimed to paint a full picture of events. It was commissioned by then Premier Tony Blair in 1998.
Northern Ireland's Deputy First Minister Martin McGuinness, who was second in command for the Irish Republican Army in Londonderry at the time, insisted the report would not lead to fresh divisions.
"My hope has to be that this is a very clear exposition of the terrible deed that was committed by the British state and the British armed forces on that day," the Sinn Fein politician said before the report's publication.
"And also that feeds into the need to ensure that we never, never again see, in any community, acts of violence such as this."
The mainly Protestant Democratic Unionist Party (DUP), whose leader Peter Robinson is Northern Ireland's first minister, has been critical of the inquiry, saying it has created a "hierarchy of victims" in Northern Ireland.
"Whilst Lord Saville was investigating Bloody Sunday, there are thousands of other victims who have seen their cases virtually ignored," said local DUP lawmaker Gregory Campbell.
"There were over 3,500 people killed during what we call the Troubles and there are hundreds of unsolved cases right across the province, yet we see hundreds of millions of pounds spent investigating less than two dozen of those deaths."
Before the report was published, around 60 relatives and campaigners held a symbolic gathering in Londonderry — known as Derry to Catholics — to complete the march halted by the killings, while a public parade was also scheduled.
