Denmark is believed to be the tenth country to be affected, with Romania and Luxembourg among the latest to report finding contaminated products.
Supermarkets in Belgium, the Netherlands and Germany have withdrawn millions of eggs from sale.
In the UK, processed foods containing eggs, including sandwiches and salads, have been recalled from Sainsbury’s, Morrisons, Waitrose and Asda.
The FSA initially thought far fewer eggs – 21,000 – had been distributed to the UK from implicated farms between March and June this year.
Prof Chris Elliott, of the Institute for Global Food Security at Queen’s University Belfast, said it was not surprising that the figure had increased by so much – and warned “the scandal isn’t over yet”.
“Often when these food scandals start to break, you start to get dribbles of information,” he told BBC Radio 4’s PM programme.
“And as the authorities in Belgium and Holland get more information they pass that onto our own Food Standards Agency.
“The potential is that number of 700,000 could increase quite a bit yet,” he added.
Should I stop eating eggs?
By James Gallagher, health and science reporter, BBC News
Fipronil should not be allowed anywhere near food.
But the risk from eggs is thought to be low, because the number of contaminated eggs is also low.
While 700,000 eggs sounds like a lot, it is worth remembering we eat 34 million every single day in the UK.
It is why the Food Standards Agency says it is “very unlikely” there is any health risk.
Many of the affected eggs will have already passed through the food chain before anyone was aware of the scandal.
And the FSA has now pulled egg sandwiches and egg salads off the shelves that were made while contaminated eggs were still being imported.
It insisted there is “no need” for people to stop eating eggs.
Fipronil, which is used to kill lice and ticks on animals, can damage people’s kidneys, liver and thyroid glands if eaten in large quantities.
Heather Hancock, FSA chairwoman, said it was not “something to worry about” and that any health impact was unlikely.
“These aren’t eggs that are in people’s fridges in the UK, these are eggs that have gone into the food chain and the level of risk to public health is very low,” she told BBC Radio 4’s World at One programme.
In an update on Thursday, the FSA said: “Some of the products made from these eggs will have had a short shelf life and will have already been consumed, however, we identified some that were still within the expiry date.”
The FSA said decision to withdraw the products was not due to food safety concerns but based on the fact that the pesticide is not authorised for use in food-producing animals.
It added: “While in some European countries eggs containing fipronil residues have been sold as fresh eggs, in the UK this is not the case.”
Aldi and Lidl stores in Germany are among the supermarkets to remove eggs from their shelves, in a move Aldi described as “purely precautionary”. Eggs sold in its UK stores were British, Aldi said.
It follows a joint investigation by Dutch and Belgian police of several premises thought to be using the substance, which can harm humans and is banned in food production.
The Netherlands is Europe’s biggest egg producer – and one of the largest exporters of eggs and egg products in the world.
The problem first surfaced earlier in August, when Aldi withdrew all its eggs from sale in Germany.
It has since emerged Belgian officials knew about the contamination in June, but did not make the information public.
More than 100 poultry farms have been closed during the investigation, and 26 suspects identified and evidence seized from their companies.
It is thought that fipronil was added to disinfectant used on some chicken farms.
The UK produces 85% of the eggs it consumes but imports almost two billion annually, the FSA said.