PSNI chief constable Sir Hugh Orde said many lives have been saved following the seizure of guns and ammunition earlier this week.
He also praised the level of co-operation between his force and the gardaí.
A total of 230 handguns, 10,000 rounds of ammunition, €450,000 in cash and drugs with an estimated street value of over €4m have now been seized in the international police operation.
Six people remain in custody in Dublin, Belfast and Amsterdam after forces from the three jurisdictions swooped on the suspected trafficking ring this week.
The PSNI chief said the operation against the criminal underworld had undoubtedly thwarted many murders, kidnappings and other violent crimes.
'We have a large number of lethal weapons that were being distributed across Europe and, in particular, our concern was Northern Ireland and our colleagues in the Republic,' he said.
The PSNI has ruled out a paramilitary link to the trafficking gang, but officers warned that guns and bullets could have found their way into the hands of dissident republican terrorists.
Earlier, two men being questioned as part of the investigation were released without charge.
The men, aged in their 30s, were arrested in Birr, Co Offaly, and Roscrea in Co Tipperary on Tuesday in follow-up searches and detained at Blanchardstown Garda station.
