The Irish government feared a "big" loyalist bomb in Dublin during a bitter unionist revolt against the Anglo-Irish Agreement, then Taoiseach Garret FitzGerald said.
In a meeting with then Northern Ireland Secretary of State Tom King just three months after the historic accord, Mr FitzGerald said people in the Irish capital were as worried as people north of the border.
"There was also a fear in Dublin of loyalist bombs and though our present information was that the loyalist paramilitaries were not yet ready to do anything big, we had to do what we could to minimise the dangers," he told the Northern Ireland secretary.
Mr King said he had been "rocked on his heels" by the unionist backlash to the agreement, signed the previous November, notes of the February meeting just declassified under the 30-year rule reveal.
He had not expected firebrand Democratic Unionist Party leader Ian Paisley to "capture and hijack" Ulster Unionist leader Jim Molyneaux along with "even ordinary moderate unionists".
Secrecy around negotiations leading up to the deal was "a disastrous mistake", he admitted.
"The unionists felt they had been treated like children and in reaction Ulster nationalism had reared its head," Mr King said, according to the State papers.
"Moderate unionists had been genuinely offended and people were now at the precipice."
In a mark of the fears of the time, Mr King said the backlash to the agreement, which gave Dublin an advisory role in Northern Ireland, could not be over-stated.
"The situation was now more dangerous than it was in 1974," he said, comparing it with the year of the Dublin and Monaghan bombings, the bloodiest atrocity of the Troubles.
"Then the average unionist sat on his hands and done nothing, thereby enabling the extremists to take over.
"Now the average unionist was very angry and prepared actively to oppose the agreement."
Mr King was trying to fend off Dublin demands for a quick and explicit implementation of the agreement, believing a more subtle approach would stand a better chance of quelling mounting unionist outrage.
Unionist MPs had resigned their seats en masse, sparking Westminster by-elections, unionist-controlled councils refused to set "rates" - a local government tax - and a widespread strike had been called in a so-called loyalist Day of Action which descended into widespread violence.
Pressure to speed up the agreement was "hard to take" in the current environment, Mr King told Mr FitzGerald.
"There was a danger of sectarian killings - that would obviously not be a benefit to the minority," he said.
He added: "Northern Ireland had to be handled with care, day by day, minute by minute."
One of the real worries was that unionist leaders "were like fireworks going off in all directions", he told the meeting.
"Many decent unionists were looking over the precipice and were worried about what they saw," he said. "But they had no leaders, no cohesion and the DUP was in disarray."
Mr King also turned his ire on the SDLP's then leader John Hume.
Mr Hume "seemed happy to let the unionists suffer" but what was "particularly despicable" was his looking forward to a confrontation between the British government and unionists.
The Secretary of State said he understood the Irish government "did not own the SDLP" but asked Mr FitzGerald if they could "persuade and cajole them".
Mr FitzGerald said he had assumed the British were keeping unionists more fully briefed about the negotiations that led to the Anglo-Irish Agreement than turned out to be the case.
A tactic of leaking details of the talks had not worked because unionists did not believe the leaks, he told the meeting.
"We had obviously got it wrong on that score," he said.