Russia has banned the import of all fresh vegetables from the European Union because of the E. coli outbreak centred on Germany.
The country's chief medical officer said EU-produced vegetables would be seized across Russia.
A leading scientist says the outbreak, which has killed 17 people in Europe, is on a scale never seen before. Infections have been reported in Sweden, Denmark, the Netherlands, Britain, Austria, Spain and Switzerland.
More than 1500 people have been infected in eight European countries, and an international row has broken out over the source of the contamination.
Earlier suggestions that infected Spanish cucumbers were the source of the outbreak have now been discounted, with German health officials admitting they do not know where this particularly virulent strain of of E.coli has come from.
The Spanish government has demanded compensation for growers forced to destroy tonnes of freshly harvested vegetables in southern Spain, and says it is considering legal action.
Denis Coulombier of the European Centre for Disease Prevention and Control (ECDC), which monitors disease in the region, said the number of cases points to a "huge contamination", probably of vegetables, at some point in the food chain.
He said infection rates should start to slow if people in Germany heed advice to avoid raw vegetables.
The head of the German public health body tackling the E. coli outbreak says it may be months before it stops, depending on whether infected food is still in warehouses and whether the original source is still active.
Reinhard Burger, president of the Robert Koch Institute, told the BBC "we may never know" the infections' source.