Garda Commissioner Noel Conroy has said he expects between 200 and 300 people to try to cause trouble during this weekend's events in Dublin to mark the historic enlargement of the European Union.
Speaking in Donegal, Commissioner Conroy said most of those intent on disrupting the celebrations were coming from Britain.
"We've been monitoring their activities as closely as we can and of course we will be receiving some assistance from other police forces in relation to the identification of those people," Conroy told reporters.
He warned: "If they actually break the law within our sight you can take it that they will be dealt with quickly and efficiently."
Gardaí will mount one of the biggest ever security operations on Saturday as European leaders fly in to Dublin for ceremonies to welcome 10 new countries to the 15-member bloc.
Some 5,000 gardaí, including 1,000 riot police with access to water cannon, will be on duty in the capital and more than 2,500 troops deployed.
Naval vessels will patrol Dublin bay, while air force helicopters will support police on the ground.