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.

In the UK, catering giant Compass Group and Whitbread, which owns hotels, coffee shops and restaurants, were the latest to say Friday that they had found horse DNA in certain beef products.

Whitbread said it was removing a meat lasagna and a beef burger from its menus and would work with the Food Standards Agency to implement a robust future testing regime.

"We are shocked and disappointed at this failure of the processed meat supply chain," it said in a written statement.

Compass Group said an affected burger from Rangeland Foods had been provided to some sites in Ireland and Northern Ireland where it holds the catering contract. It promised DNA testing across processed meat products in future.

NorgesGruppen in Norway also confirmed to CNN on Friday that horse meat had been found in frozen lasagna dishes in its stores.

"The analysis tells us that the lasagnas contained 60% or more horse meat," a spokeswoman 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 "We have withdrawn up to 8,000 products last week.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 told CNN the company had acted in good faith. "The company has never ordered horse meat and we never knowingly sold 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 for the companies involved.

Hamon said there is 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.