Taoiseach Charles Haughey urged British authorities to defer a decision to equip the Ulster Defence Regiment (UDR) with plastic bullets, declassified state papers show.
Records from his office reveal he was concerned about the deployment of the UDR in Catholic areas.
A confidential note prepared by Department of Foreign Affairs official Declan O’Donovan in 1989 shows he told British officials the decision to issue plastic bullet rounds to the UDR was unacceptable.
Mr O’Donovan added: “We are surprised that given the extreme political sensitivity of this matter, it was not broached with us before a decision was taken and we are deeply concerned that training of the UDR in the use of PBR (plastic baton rounds) at this time and the issue of them to selected units within two weeks may become a matter of controversy during the course of our general election campaign.
“This is all the more likely given the controversial incidents involving the use of PRBs in Belfast.
“The Taoiseach has personally instructed that you request a deferment of any such action by the British authorities. The Taoiseach may wish to take the matter further at ministerial level.
“The issue of PRBs to the UDR implies the appalling prospect of the UDR being drawn into situations of civil disorder.
We have been concerned for some time about deployment of the UDR in and around Catholic areas, notably in Belfast.
“The evidence coming to us — which the PRB decision tends to confirm — suggest a deliberate policy decision to move the UDR gradually into areas of potential confrontation with nationalists.”
It also emerged during a meeting in May 1989 between Northern Ireland Office officials Austin Wilson and Eric Dalzell and Irish diplomat Sean O’Huiginn that there would be no public notice about the PBR decision.
The officials told Mr O’Huiginn it would “probably attract” a hostile propaganda campaign, and that the weapons would not be visible in the UDR kit.
In a meeting between the former RUC chief constable Hugh Annesley and Noel Ryan, assistant secretary of the Department of Foreign Affairs, Mr Annesley was told the Irish government was concerned about the deployment of the UDR in nationalist areas.
In a note, Mr Ryan said: “When asked whether there were any particular initiatives he would like to see in relation to security co-operation, Mr Annesley said, somewhat tongue-in-cheek, that he looked forward to the eventual development of an all-Ireland anti-terrorist squad which he could move freely in both parts of Ireland.”