“It’s disproportionate,” Frederic Vincent, health spokesman for the European Union’s executive arm, told AFP.

“The commission will write to Russian authorities to demand an explanation. This represents between three and four billion euros in European products exported each year,” he said.

Gennady Onishchenko, the head of Russia’s consumer protection agency, said earlier that the ban had taken effect on Thursday morning and that all vegetables already shipped in from the EU would be seized across Russia.

German authorities were still searching for the source of the bacteria, which has killed 17 people, after they wrongly blamed the outbreak on Spanish cucumbers.

Enterohaemorrhagic E. coli can result in full-blown haemolytic uraemic syndrome (HUS), a disease that causes bloody diarrhoea and serious liver damage and which can result in death.

The European Commission late Wednesday lifted its warning over Spanish cucumbers that had been suspected of causing the outbreak.

It said tests carried out on cucumbers in Germany and in Spain “did not confirm the presence of the specific serotype (O104), which is responsible for the outbreak affecting humans.”