Ireland launched an intensive investigation on Sunday to establish the source of a toxic substance that forced the recall of all Irish pork products, the country's food authorities said.
The Irish government ordered the recall on Saturday of all pigmeat products made in the Republic of Ireland after dioxins were discovered in slaughtered pigs thought to have eaten contaminated feed.
The recall included products sold in Ireland and abroad.
Contaminated Irish pork was found in France and Belgium but the Food Safety Authority of Ireland (FSAI) said the problem was restricted to "Irish pigmeat related to an Irish feedstuff."
The European Commission said it was closely monitoring the situation.
The FSAI said it was almost certain that the source of the contamination was oil which mistakenly found its way into pig feed made at an Irish factory.
Dioxins are toxic chemicals that can have serious health effects, including causing cancers, if there is long-term exposure to them at high levels.
FSAI deputy chief executive Alan Reilly said dioxin levels found in meat samples were "between 80 and 200 times" above the legal limit.
But he said the risk to public health was "very, very low".
"You would have to be eating products containing these chemicals for 40 years before you would show any signs of illness."
Rhodri Evans, FSAI chief toxicology specialist, told AFP that oil was the most probable cause of the contamination and that it was "possibly" diesel oil at a plant in Ireland that used recycled bread and dough to make a pig feed.
The feed plant supplied nine pork producers.
"The profile of the dioxin we have seen would indicate it is usually associated with some sort of oil contamination," he said.
Ireland's chief medical officer, Dr Tony Holohan, said the withdrawal of all pork products from the market was "a precautionary public health measure."
The recall involves pork meat, bacon, pork sausages, sausage meat, gammon steaks, offal from pigs, salami, ham, sausage rolls, black pudding and white pudding.
The products concerned were all made since September because scientific evidence suggests the contamination was recent.
Ireland is a major exporter of pork with products sent to Britain - the main destination - and countries including Japan, Germany, Russia, France and the United States.
Laboratory tests in Britain had confirmed the presence of dioxins in both pigmeat and pig feed samples.
Evans said tests in France and Belgium had also revealed contaminated Irish pork products.
Both countries had received products from a processing plant in the Netherlands where sides of pork from Ireland were boned and processed before being shipped on.
"The initial detection was by the French authorities at import control. They did routine testing and saw a result," Evans said.
"When they saw the result they went back to the Netherlands processor and asked what's happening, where did this come from?"
Evans said the problem only involved "Irish pigmeat related to an Irish feedstuff".
The crisis is another blow to recession-hit Ireland with the agriculture ministry saying about 5,000 people work in the pigmeat industry, which is worth about 400 million euros (500 million dollars) a year.
Ireland's Europe Minister Dick Roche said the contamination was "a shock to the system" for Irish agriculture.
The European Commission said in a statement it was "closely following up this contamination incident and the actions taken to withdraw any potentially contaminated pork meat and pork meat products from the market."
EU food safety experts were to discuss the incident by telephone on Sunday and experts from countries that may have received contaminated shipments would meet on Tuesday, said commission spokesman Pietro Petrucci.