Belgium meanwhile vowed full transparency about why it kept the scandal secret despite originally learning in June about the problem involving fipronil, a substance potentially dangerous to humans.

Supermarkets in Germany, the Netherlands and Belgium have pulled millions of eggs from the shelves since Belgium gave the European Commission the first notification on July 20, while retailers in Sweden and Switzerland have followed suit.

The commission said on Monday that under its EU rapid alert system, it had been determined that eggs under suspicion of contamination had also been distributed to France and Britain via Germany.

"It's now up to the Swedish, Swiss, French and to the UK to check, because all these eggs are traceable and trackable," said spokeswoman Anna-Kaisa Itkonen.

Britain's Food Standards Agency said it was "urgently investigating the distribution of these eggs in the UK" from farms at the center of the scare, while adding that "the number of eggs involved is very small and the risk to public health is very low".

The French government said 13 batches of Dutch eggs contaminated with fipronil have been found at two food-processing factories in central-western France.

The agriculture ministry said they were unable to immediately say whether any of the products had been shipped to customers.

Meanwhile, Dutch farming organization LTO said several million hens may need to be culled at 150 companies in the country, with 300,000 having already been killed.

An LTO spokesman said they "had to be eliminated because of contamination".

Dutch authorities have shuttered 138 poultry farms - about one-fifth of those across the country - and warned that eggs from another 59 farms contained high enough levels of fipronil that they should not be eaten by children.

'Complete transparency'

Belgium currently has production blocked from 51 farms - a quarter of those nationwide - with fipronil found at 21 farms, although levels were ten times below the maximum EU limit, the country's food safety authority AFSCA said.

Belgium's agriculture minister meanwhile said he had ordered the agency to report by Tuesday on why it failed to notify neighboring countries until July 20 despite knowing about fipronil contamination since June.

Facing pressure from Germany and the Netherlands, Ducarme promised "complete transparency".

Belgian officials admitted on Saturday they had kept the problem under wraps and failed to trigger the EU's international food safety alert system, but said it was because of a fraud probe.