* Two more German farms delivered eggs with dioxin
* Source unclear, not known if linked to previous case
HAMBURG, April 5 (Reuters) - The highly-poisonous chemical dioxin has been discovered in above permitted levels in eggs from two more farms in the central German state of North Rhine Westphalia, the state agriculture ministry said on Thursday.
This followed the announcement on Wednesday that eggs with dioxin content of three to six times permitted levels had been discovered by routine tests on a third farm in the state.
The two new cases were in small farms near the central German city of Duisburg, the state ministry said. The eggs came from smallholdings which made direct sales of eggs to the public rather than sales to retailers, the ministry said.
The two smallholdings have been sealed off and are not permitted to sell more eggs and the city authorities in Duisburg have been asked to warn the public not to eat eggs from the farms, the state ministry said. One farm had 120 hens, the other 150.
How the dioxin came into the eggs is unclear and there seems to be no immediate link with the third dioxin case in the state announced on Wednesday, the ministry added.
The contamination at the two smallholdings had been discovered by routine food safety tests, it said.
In January 2011, an EU-wide health alert started when German officials said animal feed tainted with highly-poisonous dioxin had been fed to hens and pigs, contaminating eggs, poultry meat and pork at the affected farms.
Germany then introduced a series of new measures including tough restrictions on animal feed ingredients and more rigorous routine food testing.
Dioxin presents a danger to health if consumed over long periods. (Reporting by Michael Hogan; editing by James Jukwey)