Justice Minister Alan Shatter said the murder of Constable Ronan Kerr will strengthen links between police forces on both sides of the border.
Branding the killers "criminal terrorists" who are involved in robbery, extortion, smuggling and kidnapping, Mr Shatter said they would not be allowed to derail cross-community co-operation.
"The only purpose of those responsible for Ronan Kerr's murder is to cause grief and fear," he said.
"There is no noble cause to which they aspire and no ideology which can justify it."
Mr Shatter said rather than driving a wedge between communities, those behind the April 2 car bomb that killed the young policeman in Omagh, Co Tyrone, has united people against them.
The attack would not diminish the relationship built up between the Garda and the Police Service of Northern Ireland, which was "here to stay", the justice minister said.
"Far from it, it will make us even more determined to continue it, and indeed to enhance it, so as to root out these cowards and subject them to the full rigours of the law," he added.
Garda Commissioner Martin Callinan said dissident republicans behind the car bomb were getting logistical support south of the border.
He said intense pressure would be maintained on the extremists opposed to the peace process.