New questions are being raised over the contamination of eggs with insecticide in Belgium, the Netherlands and Germany, with Belgium admitting it knew about the problem in June, a month before it became public.
Officials say details were not released because a fraud case had been launched.
Katrien Stragier, a spokeswoman for the Belgian Federal Food Agency, told local television: “We’ve known since the beginning of June there’s a problem in the poultry industry with Fipronil.
“We started an investigation, we informed the justice department, because of a possible case of fraud.
“We kept it a secret for the course of the investigation. We understand people have questions about their health. We try to inform them. As soon as the investigation allows, we will offer more information on the impact on health.”
When pushed for further information, the food agency said it could not add anything further as Belgian law prohibits comment on judicial investigations.
Millions of eggs have been taken off the shelves in Germany and the Netherlands as a precaution after traces of the insecticide fipronil were found in Dutch eggs.
But in Belgium eggs have not been recalled from stores as the level of contamination was found to be below legal limits. Officials have only blocked supplies from some individual producers.
Politicians are now raising concern over who knew what, when.
John Crombez, president of the S.P.A. socialist party in Belgium, said: “Abroad they are very clear on this, in the Netherlands and Germany they are much clearer. This is important. Chickens are being sprayed with insecticides that are forbidden.
“Why didn’t we know about this before? How long has it been going on? How many eggs are being sold? They said nothing’s wrong but the supermarkets are removing them from their shelves. We need clarity and communication from the government and the federal food agency.
Germany’s agriculture minister has also expressed concern over the news that Belgium learned of the problem in June, saying he plans to raise the issue with his Belgian counterpart on Monday.
EU rules forbid the use of fipronil – which can be used for treating animals for mites and ticks – on animals that produce food.
Some reports suggest detergent used to clean out farm buildings may have been contaminated, but investigations are ongoing into how traces were found in eggs.
While there is not thought to be a major public health risk with the levels of fipronil so far detected, no chances are being taken in some places.
Poultry farms have been forced to destroy batches suspected of being contaminated and supermarket chains in Germany and the Netherlands have removed eggs from sale.
Supermarket chain Aldi removed all eggs from sale at its stores in Germany.
A number of big supermarket chains have taken Dutch eggs off their shelves, but Aldi, with more than 4,000 stores in Germany, was the first to stop all sales, regardless of origin.
Fipronil is considered by experts to be moderately toxic, with high doses causing nausea and dizziness. Very large doses can cause organ damage, especially in the kidneys and liver.
But the impact on children is more of a concern. Some reports said a child eating two fripronil-contaminated eggs in a row could pose a risk.
Prosecutors in Belgium and the Netherlands are reported to have opened investigations into possible criminal offences.