The FSA is basing its judgment on the discovery of horsemeat in Tesco frozen burgers and Findus lasagne, which it linked to suppliers in Ireland and France.
"The evidence we have about the two cases, of the significant amount of horse meat in burgers and lasagne, points to either gross negligence or deliberate contamination in the food chain," the agency said in a statement.
"In the particular cases of the Findus lasagne and the Tesco burgers, they have been withdrawn from sale. Anyone who has them in their freezer should return them to retailers as a precaution."
The organisation said in addition to its own countrywide enquiry, it was ordering the food industry to carry out testing of all processed beef products.
In Poland, alleged to be one source of horsemeat contamination, a high-level investigation has been launched - but suppliers there have denied that their products are the cause of the food scare.
A Newry firm is also continuing to defend itself after equine DNA was found in meat it was storing for another company.
Burgers supplied by Freeza Meats have consistently tested negative for horsemeat.
"As part of continual testing, further samples have been taken of our products and tested by industry authorities," a spokesman said.
"These samples have come back completely clear and the quality of our products and processes are again vindicated."
We have adhered to the highest standards of practice as a processor in the meat industry.
The spokesman added: "We call on officials in the industry - with politicians across the UK, Ireland and indeed Europe - to get to the bottom of this issue immediately, as being irresponsibly implicated in this issue has put at risk the livelihoods of almost 50 staff in Freeza Meats and the industry as a whole."
However, beef from Monaghan-based McAdam Foods, which was being held in quarantine in Freeza Meats, was found to contain up to 80% horsemeat.
McAdam Foods said it was shocked to discover the contamination in the produce, which originated in Poland.
One of country's most senior vets, who is overseeing the investigation there, said Polish traders may be the victim of fraud - he told ITN that he believed the contaminating meat did not come from Poland and that false Polish labels had been put on it.
"Today I can say that, after the inspection of local meats and lab analysis, the meat which left Poland is genuinely beef," he said.
"We are comparing the documents and labels on the meat to check if they are original or if someone has swapped or falsified them."
Nine firms in Poland are being investigated - last year one of them, Food Service, was awarded a British Standard food safety certificate.
The company's owner said it was impossible that they had been involved in the contamination and denied ever having horse products on the site.
But the contamination could have serious repercussions for Poland, in terms of both export and domestic markets.
In the meantime, the FSA has said that there is no health issue with frozen food in general and added: "We wouldn't advise people to stop eating it."