A frozen food producer caught up in a scandal over horsemeat found in beef products in the United Kingdom, Sweden and France said Saturday it will sue the Romanian producer it blames for the problem.

The French arm of Swedish frozen food firm Findus said it would file a legal complaint Monday against the unnamed Romanian business.

Findus said it had been told that its products were being made with French beef, not Romanian horsemeat.

"We were deceived," said a Findus France statement. "There are two victims in this affair: Findus and the consumer."

Also, the British arm of Findus said Saturday said it was considering legal action against suppliers, adding that early results of its internal investigation "strongly suggests" the horsemeat contamination of a beef lasagna product "was not accidental."

Meanwhile, an emergency meeting was held in London Saturday, as ministers, food inspectors and retailers grappled with a scandal that appears to be spreading across Europe.

Environment Secretary Owen Paterson said it was "completely unacceptable" that consumers were being sold food that contained horse in place of beef.

The evidence so far suggests "either criminal activity or gross negligence," he said.

Paterson warned that "more bad news" could come.

UK food businesses have been ordered to test all processed beef products for "authenticity" and report back to the authorities by Friday.

"I am determined that we get to the bottom of this and that any wrongdoing discovered is punished," said a statement by Paterson after the meeting.

Retailers in the United Kingdom, France and Sweden pulled millions of lasagna and other processed beef products off the shelves as the alarm was raised over the Findus lasagnas.

The controversy comes less than a month after horsemeat was found in hamburgers sold in the United Kingdom and Ireland. Officials in Ireland have pointed to Polish meat ingredients as being the source of horsemeat found in burgers there.

The UK Food Standards Agency said the evidence "points to either gross negligence or deliberate contamination in the food chain. This is why we have already involved the police, both here and in Europe."

An agency spokesman, Brad Smythe, told CNN that participants in Saturday's meeting had agreed that "meaningful results" must be achieved by Friday.

"This concerns products that are most likely to have been contaminated, such as beef lasagne and other budget ranges," Smythe said. The meeting was about clarifying what tests are possible, what laboratory capacity is needed, and what can be done to protect consumer confidence, he said.

"This is completely unacceptable -- this isn't about food safety but about proper food labeling and confidence in retailers," Prime Minister David Cameron said Friday, quoted on his official Twitter feed.

The revelations have thrown the meat industry into crisis and revolted many meat eaters in the United Kingdom, where horsemeat is generally considered taboo, although it is commonly eaten in neighboring France, as well as countries including China, Russia, Kazakhstan and Italy.

Findus said Thursday it had withdrawn its lasagna -- labeled with the British spelling, "lasagne" -- from UK stores Monday as a precaution after its French supplier, Comigel, raised concerns about the type of meat used.

Meanwhile, Findus France has temporarily withdrawn three ready-prepared dishes -- lasagna bolognese, shepherd's pie and moussaka -- because of the discovery of horsemeat in purported 100% beef products, the firm said. The company added, however, that the three products could still be eaten without health risk.