One soldier was being prosecuted for the murder of two men, James Wray and William McKinney, who were among 14 Catholic protesters killed by British troops in the infamous "Bloody Sunday" massacre in January 1972.

The other was to be prosecuted for the murder of 15-year-old Daniel Hegarty six months later in the same Northern Irish city of Londonderry, which is known to republicans as Derry.

"The Public Prosecution Service today announced its intention to discontinue the prosecutions of two former soldiers in connection with separate killings in Londonderry," the PPS said.

Both cases were dropped following a review of evidence triggered by a recent court ruling that caused the collapse of another murder trial involving two former soldiers.

As with that trial, these two cases were dropped as it was found that evidence gathered at the time of the killings did not meet modern legal standards.

Neither of the two British ex-soldiers had access to a lawyer when they gave their statements to military police.

"I recognise these decisions bring further pain to victims and bereaved families who have relentlessly sought justice for almost 50 years and have faced many set-backs," said Stephen Herron, Northern Ireland's director of public prosecutions.

"Legacy cases come with many challenges, particularly when they involve events which happened almost five decades ago and were not properly investigated at the time."

Prosecutions from the era of The Troubles remain fraught with controversy in Northern Ireland, despite a 1998 peace deal that ended the conflict.

Northern Ireland remains split along sectarian lines between mainly Protestant unionists who support continuing British rule over the province, and mostly Catholic, pro-Ireland nationalists.

Soldiers arrived in Northern Ireland on a mission to keep the peace in 1969 but were involved in some of the bloodiest chapters of the conflict, which saw a total of 3,500 killed on all sides.

"Bloody Sunday" has become one of the most symbolic events in the grim history of The Troubles.

A 12-year public inquiry into the shootings -- the largest investigation in UK legal history -- concluded in 2010 that British paratroopers lost control and that none of the casualties had posed a threat of causing death or serious injury.