Sweden's food safety regulator said Monday it had asked the country's prosecutors to investigate a company believed to have labelled Polish horsemeat as Swedish beef tenderloin.
"We can't say with certainty where this meat comes from because the documentation is so inadequate," Karin Cerenius of the National Food Agency's control unit told AFP.
The food security watchdog had been contacted by a consumer who was concerned over the size and colour of a beef steak she had bought.
The product was withdrawn from sale last week after tests showed it was 100 percent horsemeat.
The agency said inspections at Tallhoejden, based in Oexabaeck in western Sweden, showed the firm had insufficient procedures in place for tracking "which products entered the company, which ones leave it, and how they are labelled."
The company handled both beef and horsemeat, Cerenius said.
Tallhoejden's head of sales, Johan Sahlin, said the meat had been ordered from another Swedish company that bought it from Poland, and insisted it had been labelled as beef.
"I bought beef fillet," he said.
The scandal of horsemeat being passed on as beef has engulfed a string of European countries with millions of ready meals pulled from supermarket shelves.
The row has ensnared major international corporations including Swiss group Nestle and Swedish furniture giant Ikea.