Irish Foreign Minister Simon Coveney said it was "very concerning" that the British Conservative leader had pledged to end moves to bring criminal charges against army veterans who had served in Northern Ireland during the Troubles.

Campaigning for the December 12 election, Johnson pledged Monday, timed for the anniversary of the World War I armistice, to amend human rights law to shield servicemen from prosecutions for events before 2000.

The pledge stokes the divisive debate over prosecutions for British troops involved in killings during three decades of sectarian bloodshed in Northern Ireland.

More than 3,000 people were killed before the conflict wound down with the 1998 Good Friday Agreement, signed with the accord of London and Dublin.

"This is very concerning. Governments and parties have agreed an approach on legacy and reconciliation in Northern Ireland," Coveney said in a statement.

"There is no statute of limitations, no amnesty, for anyone who committed crimes in NI. The law must apply to all, without exception, to achieve reconciliation."

British troops were despatched to the province to buttress law enforcement in 1969, as Catholics opposed to British rule battled in the streets with Protestants who wanted to remain part of the UK.

Initially welcomed, their deployment transformed into the longest British Army operation in history and was marred by a number of high profile killings.

According to the Ulster University's Sutton Index of deaths, the British Army was responsible for around 300 killings over the course of operations, which officially ended in 2007.

But efforts to bring soldiers to justice have been fraught with acrimony and legal difficulty, and the issue continues to split British and Northern Irish society.

Some feel the prosecution of soldiers equates them with state-designated terrorists, such as those acting for the Irish Republican Army (IRA).

Others feel that an amnesty implies wrongdoing among all veterans, most of whom who served honourably.

Johnson's Conservatives have promised to protect ex-soldiers from "vexatious claims", by legislating to ensure laws intended for peace time do not apply to service personnel on military operations.

In his message to the armed forces, Johnson said: "We salute you and we will always support you."

At present there are a number of inquiries and criminal cases under way dealing with British Army killings.

Most prominently, a Parachute Regiment serviceman is currently facing murder charges for the killing of two civilians during "Bloody Sunday".

On January 30, 1972, soldiers opened fire on protesters in a majority Catholic area of the city of Londonderry, killing 14.

The case against the anonymous "Soldier F" -- who also faces four attempted murder charges -- reached court for the first time in September.