The cost of providing Defence Forces personnel for security during the visits of the Queen of England and President Obama has topped €1.7m.
The cost of Garda overtime is not yet know but it is expected to be much higher.
The Justice and Defence Minister Alan Shatter today said he does not know if it will be possible to meet the garda security costs from existing budgets.
In the Dáil he hit out at what he called a small group of "thugs" and "criminal terrorists" who prevented thousands of people from viewing Queen Elizabeth on the streets of the capital last week.
"It is unacceptable that the many thousands of people who would have wished to welcome Queen Elizabeth and Prince Phillip on our streets, and to personally view the historic events that took place during last week's visit, were largely confined to doing so on their television screens because of the threat posed by a small minority of malcontents, criminal terrorists and thugs," he said.
Meanwhile Garda Commissioner Martin Callinan has hailed the security operation during the VIP visits a success.
Commissioner Callinan thanked the public for their understanding, cooperation and support for the recent policing and security operations.
"While we tried at all times to minimise the impact of security arrangements, we know that people were inconvenienced by some of the traffic restrictions," he said.
"However we appreciate very much the fact that in the course of our work we met with goodwill and good humour from people who were entering into the spirit of the events.
"We are also both overwhelmed and humbled by the number of positive messages we have received from members of the public."