Many Jewish bodies in Europe are being bankrupted by the growing need for security measures, the US State Department's special envoy on anti-Semitism said on Friday.
Jewish communities in Europe are on edge after being targeted by Islamist gunmen in recent attacks in France and Denmark.
But even before that, many said they were victims of a growing tide of anti-Semitic crime, with the number of Jews leaving France for Israel nearly doubling between 2013 and 2014.
"Every Jewish community in western Europe certainly needs security support. Many of them are being bankrupted by the money they have to spend to protect their institutions," Ira Forman told journalists in Stockholm.
"If current trends continue, and they're not good... we have to worry about small Jewish communities in Europe and their very viability," he added.
"There is clearly a problem of integration in parts of Europe," Forman said, referring to the continent's Muslim population.
Education was key to fighting anti-Semitism since "ultimately security's a band-aid," he said.
"It's also communication strategies. How do you push back against hate on the Internet?" he said.
Forman is also due to visit Malmoe, Sweden's third largest city which suffers from a high level of hate crimes against Jews.
Jewish community leaders say the perpetrators are typically young men of Middle Eastern origin.
The US envoy will also visit Copenhagen, where last month's twin attacks saw a gunman kill a 37-year-old Jewish man outside a synagogue as well as a 55-year-old film-maker attending a debate on Islam and freedom of the press at a cultural centre.
Denmark's main Jewish organisation said last Saturday it had faced a growing security threat since 2005 but that the government had been reluctant to provide it with more funds to cover its costs.
"The whole time we have been able to demonstrate that the costs have been far greater than what (the funds) covered," former chairman Finn Schwarz told public broadcaster DR.
The Copenhagen attacks came just over a month after the January 7-9 shootings in Paris that left 17 people dead, including four Jews at a kosher supermarket.