(CNN)-- UK food safety officials have ordered the testing of all beef products following the discovery of horsemeat in beef lasagna sold by UK firm Findus, only weeks after many meat lovers were horrified to learn horse and pig DNA had been found in burgers.
Testing revealed between 60% and 100% horsemeat in the Findus lasagna, food inspectors in the United Kingdom and Ireland said.
Findus said it had withdrawn its lasagna -- labeled with the British spelling, "lasagne" -- from stores Monday as a precaution after its French supplier, Comigel, raised concerns about the type of meat used. All other Findus products are unaffected, it said.
Horse, pig meat found in frozen burgers The latest discovery comes less than a month after the Food Safety Authority of Ireland found that 10 out of 27 hamburger products it analyzed in a study contained horse DNA, while 23 of them tested positive for pig DNA.
In nine out of the 10 burger samples, the horse DNA was found at very low levels, the inspectors said, but in one sample from Tesco, Britain's largest retailer, the horse meat accounted for about 29% of the burger.
The revelation prompted the withdrawal of millions of burgers from supermarket shelves.
The uproar over dubious processed meat has international ramifications, with companies in Poland and France involved as well as some in the United Kingdom and Ireland.
In the wake of the Findus discovery, the chief executive of the Food Standards Agency, Catherine Brown, said UK firms must test all their beef products by next Friday.
"The FSA is now requiring a more robust response from the food industry in order to demonstrate that the food it sells and serves is what it says it is on the label," she said.
"We are demanding that food businesses conduct authenticity tests on all beef products, such as beef burgers, meatballs and lasagne, and provide the results to the FSA. The tests will be for the presence of significant levels of horse meat."
While horsemeat itself is not considered a food safety risk, its unauthorized use in certain products has raised concerns it could contain the veterinary drug phenylbutazone, or "bute," commonly used to treat horses.
Meat from animals treated with phenylbutazone is not allowed to enter the food chain as it may pose a risk to human health.
Findus has been ordered to test the lasagna withdrawn from the shelves for the drug's presence.
The Food Safety Authority of Ireland said Friday that the affected Findus lasagna had also been sold in Ireland. It urged consumers not to eat them, but to return the product to the store.
Findus issued a statement Thursday saying it is confident it has fully resolved the "supply chain issue" that led to the discovery of horsemeat in its lasagna.
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"We understand this it is a very sensitive subject for consumers and we would like to reassure you we have reacted immediately. We do not believe this to be a food safety issue," the firm said.
"Fully compliant beef lasagne will be in stores again soon."
Horsemeat is generally considered taboo in Britain, although it is commonly eaten in neighboring France and other countries, including China, Russia, Kazakhstan and Italy.
The discovery of pig DNA in beef products is of particular concern to Jews and Muslims, whose dietary laws proscribe the consumption of pig products. Jewish dietary laws also ban the eating of horsemeat.
The Justice Ministry confirmed last week that a number of meat pies and similar items supplied to prisons in England and Wales were labeled and served as halal -- prepared in compliance with Islamic dietary law -- but contained traces of pork DNA, the Food Standards Agency said.
"This is an unacceptable situation and people have a right to expect that the food they are eating is correctly described," the agency said.
The furor over the Findus lasagna prompted humor as well as outrage on Twitter.
"If you think the Findus Lasagnes are bad, you should try their Filly Cheese Steak," wrote James Martin, posting as @Pundamentalism.
Comedian Adam Hills, posting as @adamhillscomedy, joked: "Those horses wanted to be uncovered in British Lasagne. Even the brand was called Findus."