Tánaiste and Minister for Foreign Affairs Eamon Gilmore criticised British Prime Minister David Cameron over his refusal to order a public inquiry into the controversial murder of Belfast solicitor Pat Finucane.
Mr Gilmore accused London of falling short of a deal struck at the Weston Park peace talks in 2001.
Mr Gilmore said Dublin had already conveyed its dissatisfaction and disappointment and would be preparing a formal response in the coming days.
"There are sometimes occasions when frank disagreements arise between states," he said.
"This is one on this occasion."
The Finucane family walked out on a meeting with Mr Cameron at Downing Street last Tuesday when he told them he would ask a senior barrister, Desmond de Silva QC, to review the files into the killing rather than set up a full inquiry.
Mr Gilmore said Taoiseach Enda Kenny was only told about the decision during a telephone call from Mr Cameron shortly before the meeting.
Both Mr Kenny and Mr Gilmore have expressed their dissatisfaction personally with Mr Cameron and Northern Ireland Secretary of State Owen Paterson.
The Finucane family's legal team will work with Government officials in the coming days on their contacts with the British government in recent months ahead of a formal response from Dublin. Top level meetings are expected to follow.
Mr Gilmore said Ireland had an agreement with Britain over the investigation of certain murders involving alleged State collusion during the Troubles with which Mr Cameron's government had to comply.
"It is our view that what has been proposed by the British government falls short of that," he said.
Speaking after a meeting with Mr Gilmore in Dublin, Pat Finucane's widow Geraldine said he had described last Tuesday's decision as a dark day for her family, the country and the rule of law.
"I do believe the Government are as upset about what happened on Tuesday as the family are," she said.
Mrs Finucane said she was disappointed Taoiseach Enda Kenny could not make the meeting but said it was clear anything Mr Gilmore was pledging had the full backing of the Taoiseach.
Michael Finucane, son of Pat Finucane, described the fallout as a significant diplomatic incident.
Mr Finucane said the British government had reneged on a bi-lateral political agreement and he understood the Irish government was seeking the legal advice of the Attorney General.
On the possibility of taking their case to an international court, he said: "Such a step would require detailed consideration and legal advice, but I would imagine it is one option."
Mr Finucane said the British government had misled his family, the media and the Irish government.
"At the very least their actions are disingenuous in the extreme," he added.
A masked gang from the loyalist Ulster Defence Association (UDA) shot Pat Finucane in front of his wife and three children as they ate dinner in their north Belfast home in 1989.
The British government has admitted there was state collusion in the murder.