Brussels - Dutch investigators arrested two suspects on Thursday from a firm at the centre of a probe into insecticide-tainted eggs as European authorities stepped up efforts to tackle the widening scandal.
The arrests during joint raids by Belgium and the Netherlands came as Britain said it had imported 700 000 eggs from Dutch farms linked to fears over fipronil contamination, far more than first thought.
The spiralling scandal also spread to Luxembourg, the eighth country affected by a scare that has seen millions of eggs destroyed or taken off the shelves across Europe.
Fipronil is commonly used to get rid of fleas, lice and ticks from animals but is banned by the EU from use in the food industry. It can harm people's kidneys, liver and thyroid glands.
With questions growing about how the contamination happened and whether consumers have been kept in the dark, pressure has grown on the two countries at the centre of the scandal - the Netherlands and Belgium.
Dutch prosecutors said they had arrested "two managers at the company that allegedly used the substance at poultry farms," with Dutch media naming the suspects' company as Chickfriend.
Farmers in the Netherlands - one of Europe's biggest egg exporters - and Belgium have previously identified Chickfriend as the company that they hired to treat their chickens to eradicate the parasite red lice.
The Dutch authorities said the raids also also focused on a Belgian supplier of fipronil, named in the media as Poultry-Vision, and another Dutch company that colluded with it, which was not identified.
"They are suspected of putting public health in danger by supplying and using fipronil in pens containing egg-laying chickens," prosecutors' spokesperson Marieke van der Molen said.
Belgian investigators meanwhile identified 26 people or companies as suspects during the 11 raids by police and food safety agency officers, for offences including fraud and breaking EU food laws.
Investigators seized paperwork, cars, banking details and fixed assets in both countries. They said they had also seized 6 000 litres of "prohibited products" in Belgium.
The joint offensive came despite Belgium earlier accusing the Netherlands of knowing about the problem of fipronil in eggs since November 2016, but failing to inform them until July.
The Netherlands denied the charge.
Meanwhile British authorities said that around 700 000 eggs from Dutch farms implicated in the scandal had been distributed in Britain, just days after saying the number was only 21 000.
As a result, four major British supermarket chains have withdrawn some products containing eggs, including sandwiches and salads, the Food Standards Agency said.
"It is likely that the number of eggs that have come to the UK is closer to 700 000 than the 21 000 we previously believed had been imported," the agency said.
It played down the risk to public health saying this number represents just 0.007 percent of the eggs consumed in Britain every year.
Luxembourg said eggs sold in branches of the discount supermarket Aldi had been withdrawn, with one batch containing so much fipronil it was unsafe to be eaten by young children.
Aldi earlier this month pulled all Dutch eggs from its stores in Germany.
Tests also found fipronil in eggs sold in Luxembourg supermarket chain Cactus, which had originally come from the Netherlands, while two Luxembourg suppliers of prepared meals, Caterman and Carnesa, said they had received cartons of liquid eggs from a contaminated source in Belgium.
Some of those eggs had been used in minced beef and luncheon meat but the items had been removed, they said.
The eggs at the centre of the scandal have mainly come from the Netherlands, followed by Belgium and Germany. Scores of farms have been shut.
Sweden, Switzerland, Britain, France and Luxembourg have also now announced that they have found contaminated eggs.
The problem is believed to stem from a substance used by Dutch company Chickfriend which farmers in the Netherlands and Belgium say they hired to treat their chickens.
A lawyer for Poultry-Vision has said the firm sold it to Chickfriend but has not said where it got the substance.
The French government says a Belgian company - which it did not identify - mixed fipronil with another, lawful, substance.