LONDON (CNN) -- A Europe-wide scandal over horse meat in products labeled beef spread still further Friday, as UK authorities revealed the results of DNA testing on beef products and raided the premises of three more UK food firms.
News of the raids came as the first results of tests ordered by the UK Food Standards Agency on beef products across the industry were released.
Of 2,501 tests carried out by noon Friday, 2,472 proved negative for horse above 1 percent, the agency said.
Another 962 tests are still under way, the agency said at a news conference. More than 10,000 products remain to be tested.
The 29 positive tests involved seven different products, sold by five suppliers, according to the Food Standards Agency.
Fifteen of the positive tests were for the lasagna products sold by frozen food giant Findus that first triggered the horse meat alert last week.
The others concerned beef products sold by supermarket chains Tesco, ALDI and the Co-operative, and burgers made by catering supplier Rangeland.
The agency declined to give details of the names or location of the three food premises raided Friday.
Investigations are ongoing, but authorities cannot rule out the possibility of arrests, it said.
The latest raids come a day after UK authorities arrested three workers at two meat plants, Farmbox Meats near Aberystywth and Peter Boddy Slaughterhouse in Todmorden, West Yorkshire.
Inspectors toured the plants Tuesday and suspended their permits to operate Wednesday, the agency said.
Meanwhile, authorities in northern England confirmed Friday that a dish had been pulled from 47 school kitchens after tests revealed horse DNA.
The ready-made cottage pie, or shepherd's pie, came from an external supplier, Lancashire County Council said.
"This does not appear to be a food safety issue but I've no doubt parents will agree we need to take a very firm line with suppliers," councilor Susie Charles said in a statement.
Authorities across Europe have been scrambling to get a grip on the crisis over rogue horse meat in beef products.
The European Union intends to begin testing meat across all 27 member states, it announced Friday.
The EU called for testing 10 to 150 samples per country and at least five tests per country for the presence of the drug phenylbutazone, also known as bute, which is approved for horses but is not allowed to enter the food chain because it can be harmful to humans.
Over the past week, unauthorized horse meat has been discovered in a variety of products labeled as beef that were sold in supermarkets in countries including Britain, France, Sweden, Switzerland, Germany and Ireland.
A spokeswoman for NorgesGruppen in Norway confirmed to CNN on Friday that horse meat had also been found in frozen lasagna dishes in its stores.
"The analysis tells us that the lasagnes contained 60% or more horse meat," she said. "We have withdrawn up to 8,000 products last week. We are in talks with the factory, the French company Comigel."
Comigel was one of two French firms whose role in the scandal was highlighted at a news conference held by French authorities Thursday.
The other firm, Spanghero, should have known that the meat it labeled as beef was actually horse, French Consumer Affairs Minister Benoit Hamon said.
Spanghero was the first company to label the meat as beef, the minister said, adding that 750 tons of horse meat were involved over a period of at least six months.
Spanghero should have identified the meat as horse from its Romanian customs code, as well as its appearance, smell and price, he said.
Comigel also should have noticed anomalies in labeling of the meat it received, Hamon said.
A Spanghero representative said the company acted in good faith. "The company has never ordered horse meat and we never knowingly sold on horse meat," the representative said.
The affair has been passed to the Paris prosecutor to be investigated as fraud, Hamon said. The offense is punishable by up to two years in prison and fines of up to 187,500 euros for the companies involved.
Hamon said there was no reason to doubt that the Romanian abattoir that supplied the horse meat was acting in good faith.
In another twist, UK inspectors said Thursday that horse carcasses contaminated with the equine painkiller bute may have entered the food chain in France. UK and French authorities are working to trace the horse meat, the Food Standards Agency said.
The meat industry was first thrust into the spotlight last month when Irish investigators found horse and pig DNA in hamburger products. The discovery of pig DNA in beef products is of particular concern to Jews and Muslims, whose dietary laws forbid the consumption of pork products. Jewish dietary laws also ban the eating of horse meat.
CNN's Claudia Rebaza, Kendra Wates and Susannah Palk contributed to this report.
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