Newly released test results on a batch of contaminated German animal feed suggest it contained more than 77 times the approved amount of dioxin.

Some 4,700 German farms have been shut after tests in Schleswig-Holstein found excessive levels of the toxic chemical.

Initially the scare was confined to Germany, but then it emerged that a batch of eggs had been exported to Holland and from there to Britain.

South Korea has blocked imports of German pork and poultry products.

German officials are investigating possible "illegal activity" after a company allegedly supplied 25 animal feed makers with 3,000 tonnes of contaminated fatty acids.

Officials have traced the contamination to the Harles und Jentzsch plant in the northern state of Schleswig-Holstein, where oils intended for use in biofuels were distributed for use in animal feed.

"The first indications point to a high level of illegal activity," said a spokesman for Agriculture Minister Ilse Aigner on Friday.