Threatening letters containing shotgun cartridges have been sent to two Government ministers and a number of fertility clinics around the country.
Minister for Health Mary Harney and Minister for Enterprise, Trade and Employment, Micheál Martin, both received letters claiming to be from a previously unknown group, the Irish Citizens Defence Force.
The letter to Ms Harney was delivered to the minister's office at the Department of Health headquarters at Hawkins House in Dublin on 29 February.
A letter containing a live shotgun cartridge was also received by a number of fertility clinics, including the Clane Clinic in Kildare on the same day.
Management at the clinic told RTÉ News that it contained threats to staff and was deeply upsetting.
The clinic says it has taken precautions as a result of the letter.
The SIMS Fertility Clinic in Dundrum said it also received a device and letter.
Dr Tony Walsh of the SIMS fertility clinic said the event had been very upsetting for staff and pregnant women in the clinic at the time.
He described the sending of threatening letters and devices to fertility clinics around the country as an act of social terrorism.
The Garda Commissioner has appointed a detective inspector to examine the incidents.