Dissident republican groups continue to pose a significant threat and do not need large weapons stores to prosecute their campaign, the Garda Commissioner, Mr Pat Byrne, said.
Speaking to reporters at a graduation ceremony at the Garda College, Templemore, Co Tipperary, he said the Omagh bomb had used fertiliser which was easily obtainable.
Despite the threat from dissidents, the Provisional IRA leadership remained in control of its organisation and IRA arms dumps remained under the control of the IRA leadership. He said no dissident group in "their right mind" would touch one of these dumps.
Politicians in the North have welcomed the discovery of a firing range and the arrest of 10 dissident republicans in north Co Dublin.
The Alliance Party leader, Mr Sean Neeson, said: "Clearly, there are those people that are opposed to democracy and for that reason the security services on both sides of the Border must be given every help to take these people out of operation."
The DUP Assembly member for Newry and Armagh, Mr Paul Berry, also welcomed the arrests. "I most certainly welcome this find and I'm glad that this training camp has been caught by the Garda service. I am calling on security to be stepped up immediately, specially around the Border areas of Newry, Armagh and Fermanagh."
The RUC Chief Constable, Sir Ronnie Flanagan, has repeated warnings that a growing threat exists from dissident republicans. He said his force had little doubt they were planning attacks, particularly along the Border.
However, there was no evidence of co-operation between the Provisional IRA and the dissidents, he added. In fact, there were "some signs recently of increasing friction", he said.