Four UK supermarkets withdrew products from their shelves on Thursday after it emerged that 700,000 eggs from Dutch farms had been distributed to Britain.
The substance can damage people's kidneys, liver and thyroid glands if eaten in large quantities.
More than 180 Dutch chicken farms were closed amid follow-up examinations.
Fipronil is a popular insecticide to treat pets for fleas and ticks but it is forbidden for use in the food chain.
Millions of eggs have been recalled in eight countries across Europe in the past week.
A batch of 196,000 contaminated Belgian eggs was put on sale between April and May and consumed "without any observed health impact", the French agriculture ministry said.
The European Commission said on Friday a total of 15 countries have been affected by the fipronil-contaminated eggs, including two non-EU countries, Switzerland and Hong Kong.
The European Commission confirmed that all these countries had received eggs that had traces of the insecticide fipronil.
Fipronil is commonly used in veterinary products to get rid of fleas, lice and ticks but it is banned by the European Union from being used to treat animals destined for human consumption, such as chickens.
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