France promised the results of an urgent inquiry into the scandal within days and the government announced crisis talks with meat industry representatives for Monday night.
As Britain dismissed calls for a ban on EU meat, producers and distributors insisted they had been deceived about the true nature of the meat and vowed to take legal action.
Several ranges of prepared food have been withdrawn in Britain, France and Sweden after it emerged that frozen food companies had used horsemeat instead of beef in lasagne, other pasta dishes, shepherd's pies and moussaka dishes.
Reflecting the complexity of European food supply chains, the meat has been traced from France through Cyprus and The Netherlands to Romanian abattoirs.
Officials in Bucharest announced an urgent inquiry on Saturday. On Sunday, President Traian Basescu said he feared his country "would be discredited for many years" if a Romanian meat supplier was found to be at fault.
French retailers Auchan, Casino, Carrefour, Cora, Monoprix and Picard announced Sunday they were withdrawing products provided by frozen food giant Findus and French producer Comigel over the horsemeat concerns.
The retailers said the withdrawal was the result of "labelling non-compliance in regards to the nature of the meat" in the products.
French Consumer Affairs Minister Benoit Hamon said officials would have the preliminary results of their inquiry into the scandal by Wednesday. France "will not hesitate" to take legal action if there is evidence that companies had knowingly duped consumers, he added.
His ministry said Hamon and other senior officials would meet with "all players in the industry" for crisis talks on the scandal on Monday.
Foreign Minister Laurent Fabius also made it clear someone would have to pay for what he described as a "abominable and disgusting" affair.
"There are clearly people involved making a profit... there need to be tough sanctions." he told France's BFMTV television.
Findus has said it will file a legal complaint in France after evidence showed the presence of horsemeat in its supply chain "was not accidental". Its Nordic branch said Sunday it planned to sue Comigel and its suppliers.
"This is a breach of contract and fraud," said the head of Findus Nordic, Jari Latvanen. "Such behaviour on the part of a supplier is unacceptable."
Comigel head Erick Lehagre told AFP the company had been fooled by its suppliers and vowed to seek compensation.
"We were victims and it's now clear that the problem was not with Findus nor with Comigel," he said. "This represents a very heavy loss for us and we will seek compensation."
In Britain, tests have found that some frozen ready meals produced in mainland Europe and labelled as processed beef actually contained up to 100 percent horsemeat.
But Food Minister Owen Paterson dismissed calls for a ban on EU meat imports, describing the idea as a "panic measure".
"Arbitrary measures like that are not actually going to help. Firstly we are bound by the rules of the European market," he told Sky News television.
But he added: "Should this move from an issue of labelling and fraud and there is evidence of material which represents a serious threat to human health, I won't hesitate to take action."
Anne McIntosh, the head of the British parliament's food affairs scrutiny panel, had called for the ban. A moratorium was needed until "we can trace the source of the contamination and until we can establish whether there has been fraud", she argued.
The scandal has had particular resonance in Britain, where eating horsemeat is considered taboo. British authorities have also said they are testing to see whether the horsemeat contains a veterinary drug that can be dangerous to humans.
The Findus meals were assembled by Comigel using meat that was provided by Spanghero, a meat-processing company also based in France. Comigel supplies products to companies in 16 countries.
Spanghero in turn is said to have obtained the meat from Romania via a Cypriot dealer who had subcontracted the deal to a trader in The Netherlands.
A Romanian food industry official pointed the finger of blame at the French importer, saying it was up to that company to verify the meat.