Beansprouts grown in northern Germany are suspected to be the source of an E. coli outbreak that has left 22 people dead, local officials say.
The agriculture minister for Lower Saxony, Gert Lindemann, said there was a clear trail of evidence pointing to a plant nursery south of Hamburg.
The nursery has been closed, though officials say the outbreak's source cannot yet be definitively confirmed.
Germans are being advised to stop eating the beansprouts.
The BBC's Stephen Evans in Berlin says the announcement may cause embarrassment to German authorities, who had earlier pointed to Spanish farms as the source of the outbreak.
More than 2,150 people in Germany have been infected by enterohaemorrhagic E. coli (EHEC) bacteria. Many have developed haemolytic-uraemic syndrome (HUS), which can be fatal.
Cases have been concentrated in the northern city of Hamburg, with infections in 12 other countries linked to travel in Germany.
Twenty-one of the victims have died in Germany, and one person in Sweden.Used in salads
Mr Lindemann said epidemiological studies all seemed to point to the plant nursery in Uelzen in the state of Lower Saxony, about 100km (62m) south of Hamburg - though official tests had not yet shown the presence of the bacteria there.
"Further evidence has emerged which points to a plant nursery in Uelzen as the source of the EHEC cases, or at least one of the sources," he said.
"The nursery grows a wide variety of beansprouts from seeds imported from different countries."
The beansprouts include adzuki, alfalfa, broccoli, peas, lentils and mung beans, all grown in the nursery for consumption in salads.
Gert Hahne, a spokesman for the Lower Saxony agriculture ministry, earlier told the Associated Press news agency that many restaurants in which people ate before becoming ill had recently taken delivery of the sprouts.
He said authorities would still maintain a warning against eating tomatoes, cucumbers or lettuce.
The health ministry in Berlin said it was still waiting for results from tests on the beansprouts, Germany's DPA news agency reported.
And the head of the Robert Koch Institute (RKI), Germany's national disease centre, was also reported as saying that the cause of the outbreak could not yet be confirmed.
Scientists say the new E.coli strain is an aggressive hybrid form toxic to humans and not previously linked to food poisoning.
German federal Health Minister Daniel Bahr said hospitals in northern Germany were overwhelmed by the outbreak, though he said medical workers were doing "everything necessary" to help patients.
On Saturday, German officials said there were signs that the outbreak was slowing.