The fraud that caused the contamination of millions of eggs with the insecticide fipronil began in September 2016 and has now affected 34 countries, the EU said on Thursday.
Millions of eggs have been pulled from supermarket shelves and dozens of poultry farms closed, with the European Commission due to hold a crisis meeting in September.
"We have now indication that this illegal use of fipronil ... started as far as we know in September 2016," said Sabine Juelicher, Director for Food Safety at the European Commission, the EU's executive arm.
The commission said the insecticide has now been discovered in eggs in 22 of the 28 EU countries, plus other European countries Switzerland, Norway and Liechtenstein.
Fipronil was also detected in nine non-European countries including Hong Kong, Russia, Saudi Arabia and Iraq.
Commonly used to get rid of fleas, lice and ticks from animals, fipronil is banned by the European Union from use in the food industry.
The problem is believed to stem from a substance used by a Dutch company, Chickfriend, which farmers in the Netherlands and Belgium say they hired to treat their chickens.
Two Chickfriend managers are being held in the Netherlands on suspicion they endangered public health by using the insecticide, fipronil, at Dutch poultry farms.
The fraud was mainly practised in the Netherlands and Belgium, where nearly 350 farms were temporarily closed by authorities earlier this month.
The discovery sparked a row between the countries and Germany about how long officials knew about the problem.
Belgium has accused the Netherlands of having detected contaminated eggs as far back as November but keeping it quiet. The Netherlands has said it was tipped off about the use of fipronil in pens but did not know it was in eggs.
Belgium became the first country to officially notify the EU's food safety alert system on July 20, but the news did not go public until August 1.
The EU insists there is no threat to humans, but the World Health Organization says that when eaten in large quantities it can harm people's kidneys, liver and thyroid glands.
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