Beef burgers being sold in the UK and Ireland have been found to contain horse meat, the Republic of Ireland's food safety authority (FSAI) says.
The meat came from Liffey Meats and Silvercrest Foods in Ireland and Dalepak Hambleton processing plant in the UK and was on sale in Tesco, Iceland, Lidl, Aldi and Dunnes Stores.
The FSAI found that of the 27 beef burger products that were tested, 10 contained horse DNA and 23 were positive for pig DNA.
While nine out of 10 beef products showed low levels of horse DNA, one sample from Tesco showed that horse accounted for 29 per cent of the meat.
Traces of horse meat were also found in raw ingredients imported from Spain and the Netherlands.
The retailers are pulling all batches of the meat today.
FSAI chief executive Alan Reilly said while consumers "should not be worried", as the findings didn't pose a health risk, they did raise concerns.
"Whilst, there is a plausible explanation for the presence of pig DNA in these products due to the fact that meat from different animals is processed in the same meat plants, there is no clear explanation at this time for the presence of horse DNA in products emanating from meat plants that do not use horse meat in their production process.
"In Ireland, it is not in our culture to eat horse meat and therefore, we do not expect to find it in a burger. Likewise, for some religious groups or people who abstain from eating pig meat, the presence of traces of pig DNA is unacceptable.
Reilly said FSAI was working with the meat processing plants and the department of agriculture and fisheries to work out how the horse DNA had made its way into the products.
The testing was done as part of a number of annual routine surveys and studies on food safety, the FSAI said.
New Zealand had its own horse meat scandal in 2009 when Food Safety New Zealand took action against Tuakau Pet Food Abbatoir for illegally selling horse meat to Aucklanders.
Manufactured for pets, the horse meat products were being sold in South Auckland markets.
The sale of unsafe meat in New Zealand comes with a penalty of $500,000