Millions of Dutch eggs have been declared unsuitable for consumption as they contained high quantities of fipronil.

The Dutch food and product safety board (NVWA) revealed the scandal and raised the alarm last week about eggs that have been contaminated and pose a severe threat to consumers.

Fipronil is an insecticide used against lice, ticks and fleas. For the World Health Organisation (WHO), fipronil is "moderately toxic" but in high concentrations, it could have dangerous effects on kidney, liver and thyroid gland function.

EurActiv reports that manufactured by Germany’s BASF among other companies, fipronil is commonly used in veterinary products to get rid of fleas, lice and ticks.

But it is banned from being used to treat animals destined for human consumption, such as chickens.

European Commission spokeswoman Anna-Kaisa Itkonen told reporters last week that developments were being monitored "very closely".

"What I can say is that the farms are identified, the eggs are blocked, the contaminated eggs are traced and withdrawn from the market, and the situation is under control," she said.

It is believed the substance was introduced to poultry farms by a Dutch business, named Chickfriend, which was called in to treat red lice, a nasty parasite in chickens.

It said that it used a pesticide it got from a Belgian supplier and now there is an ongoing investigation about whether the Dutch company was aware of the toxic insecticide.

"We knew"

While supermarkets in the Netherlands and Germany have massively withdrawn batches of eggs from their shelves, Belgium admitted that it was aware of the case as early as June.

"We have known since early June there was potentially a problem with fipronil in the poultry sector," Belgium’s food safety agency spokeswoman Katrien Stragier told the BBC.

"We immediately launched an investigation and we also informed the prosecutor because it was a matter of possible fraud," she added but did not elaborate.

The statement prompted the reaction of German Agriculture Minister Christian Schmidt who expressed concerns over the possible contamination. He said he planned to call his Belgian counterpart on Monday to discuss the situation.

"Agriculture Minister Schmidt would have expected notification [about the contamination] from officials in Belgium in a timely and comprehensive manner," a ministry spokesman said.