The Irish police has been called in to assist with investigations into the horse meat contamination scandal, after a meat filler containing 75% horse DNA was found in Ireland.

The raw material – which had not yet been used to make burgers – was discovered by Irish officials at Rangeland Foods in County Monaghan. The Irish department for agriculture, food and the marine said the material had been labelled as being from Poland and was imported through a meat trader based in Ireland.

Irish agriculture minister Simon Coveney said the discovery at Rangeland – coupled with current investigations into horse DNA contamination at ABP Food Group’s Silvercrest plant – had prompted him to ask the Gardai “to join the investigation team”. He added his department’s special investigation unit was now also involved.

Production at Rangeland, which describes itself as, “the number one producer of beefburgers to the foodservice industry”, has been suspended as investigations continue. Silvercrest also remains closed.

A spokeswoman for Rangeland said the Polish material that tested positive for horse DNA had been received in early January and did not go into production. She added that 90% of the beef used by Rangeland was from Ireland.

The discovery of horse DNA at Rangeland comes as the UK’s Food Standards Agency announced it had found horse meat in frozen meat stored in a cold store in Northern Ireland, owned by Freeza Meats, with two samples containing 80% horse DNA. It said the product did not enter the food chain.

A spokeswoman for the FSA said, unlike officials in the Republic of Ireland, the FSA had not asked the police to get involved at this stage but added this might happen in the future, if necessary.

The FSA also said Freeza was “potentially linked” to Silvercrest but did not elaborate further on what those links might be. ABP Food Group has issued a statement stressing Freeza is not part of ABP but did not comment further.

Freeza Meats said the meat tested by the FSA had been stored there on behalf of meat trader McAdam Foods from County Monaghan. It stressed none of Freeza Meats’ products had tested positive for horse DNA.