As consumers across Europe weighed whether it was safe to eat raw produce, Russia extended a ban on fresh vegetable imports, initially imposed on produce from Spain and Germany, to encompass all of the European Union on Thursday, triggering a sharp response from European officials who called the move “disproportionate.”

Britain’s Health Protection Agency, meanwhile, confirmed Thursday that the number of cases in Britain had risen from three to seven, with the bacteria found in people who had recently traveled to Germany. For the first time, it said, three residents of Britain were among those infected. There had been no cases of secondary infection, the agency said.

In Geneva, Gregory Hartl, a spokesman for the World Health Organization, said: “What we understand is this is a strain which has never been detected in an outbreak situation before.” He said scientists at “many laboratories” were working to gather more information about the strain. The origins of the outbreak, which has killed at least 17 people — 16 in Germany and a Swede who visited there recently — remains unknown.

In a statement on Thursday, a Chinese laboratory collaborating with German scientists said the contagion had been caused by a “new strain of bacteria that is highly infectious and toxic.” The strain carries “several antibiotic resistant genes,” according to the Beijing Genomics Institute in the southern city of Shenzen, “which makes antibiotic treatment extremely difficult.”

The statement referred to the strain as “entirely new” and “super-toxic” and said it was similar to a strain known as EAEC 55989 found in the Central African Republic and known to cause serious diarrhea. The Chinese laboratory had been working with scientists at the University Medical Center Hamburg-Eppendorf at the epicenter of the outbreak.

“The situation is still tense,” said Jörg Debatin, director of the Hamburg-Eppendorf facility. “At the beginning of the week we had been hoping to see a trend towards fewer infections, but that has not happened.”

Holger Rohde, a bacteriologist at the same medical center, said tests conducted with the Chinese scientists in Shenzen had shown that the new strain was a hybrid that caused the virulent complication of E.coli known as hemolytic uremic syndrome, or HUS, which attacks the kidneys and can be lethal.

“This is a genetic combination we have not seen before,” he said. About 80 per cent of the genetic composition derived from the E.Coli strain 0104. But the other 20 per cent came from another more toxic bacterium.

Louise Brown, a spokeswoman for Britain’s Health Protection Agency, said the strain of E.coli causing the outbreak “has a combination of characteristics that have not been identified in strains that have caused illness before.”

The most striking difference with previous contagions was that “large numbers of people between 16 and 60” have developed HUS. “The evidence that is already available tells us that the German authorities have been dealing with something new,” she said in an e-mailed statement.

In recent days, the European Center for Disease Control and Prevention, a European Union agency based in Stockholm, and other health authorities in Europe have blamed the outbreak on a rare strain of E. coli called O104:H4.

Since 2008, there have been only eight cases linked to that strain reported in the European Union, according to the agency, whose Web site was still reporting on Thursday that laboratory results indicated O104:H4 carried in contaminated food was “the causative agent” of the outbreak in Germany and had also been detected in Denmark.

Quite apart from health concerns, the impact of the outbreak spread increasingly to European politics and the continent’s economic relations.Russian news reports quoted health officials as saying Moscow’s ban on European produce would begin immediately. If strictly enforced, the prohibition would magnify the woes of European Union farmers since Russia ranks among their biggest markets. Farmers in Germany and Spain have already complained that public fear of contagion has forced them to destroy their crops.

“What Russia is doing is disproportionate,” Frederic Vincent, the spokesman for the European Union’s Health Commissioner John Dalli, said Thursday. He said the commission would send a letter later Thursday to Moscow explaining why Russia should remove the restrictions. Russia relies on imports from the European Union for up to 40 percent of its fruits and vegetables and the market is worth up to $5.5 billion annually, according to the commission.

Alan Cowell reported from Berlin, and James Kanter from Brussels. Reporting was contributed by William Neuman from New York; Victor Homola, Stefan Pauly and Judy Dempsey from Berlin; and Raphael Minder from Motril, Spain.

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