In a statement, Downing Street said the PM described the findings about the killings, known as the 'Ballymurphy massacre,' as "deeply sad" and "tragic."

"The Prime Minister apologised unreservedly on behalf of the UK Government for the events that took place in Ballymurphy and the huge anguish that the lengthy pursuit of truth has caused the families of those killed," the statement read.

Johnson said the government intended to "deliver" for victims of the violence in Northern Ireland and to safeguard the "gains made through the Belfast/Good Friday Agreement."

The Good Friday Agreement was signed in 1998 to bring about peace in Northern Ireland after three decades of conflict between Irish nationalists, British unionists and British soldiers.

On Tuesday, Justice Siobhan Keegan said nine people killed by the British Army in the Ballymurphy area of west Belfast in August 1971 were "entirely innocent" and that claims they were paramilitaries were "wrong."

Soldiers involved in the shootings had claimed they were firing on gunmen.

A total of 10 people were killed in the incident, but Keegan said there was not enough evidence to say with certainty who was responsible for the death of the tenth victim, John James McKeer, and criticised authorities' failure to investigate his death thoroughly at the time.

An eleventh person died of a heart attack during the incident.

Johnson's office also said that the PM had spoken with the First Minister of Northern Ireland Arlene Foster and Deputy First Minister Michelle O'Neill about the findings of the judge-led inquiry on Wednesday.