Anti-Semitism has grown during the coronavirus pandemic, particularly online, a new EU report said on Tuesday, but gaps in data make it difficult to measure how bad the problem really is.
As well as old lies being revived, "new anti-Semitic myths and conspiracy theories that blame Jews for the pandemic have come to the fore", said the report.
"Anti-Semitism, especially online, grew during the pandemic," said the report, by the European Union Agency for Fundamental Rights (FRA).
At the same time, the agency's own research showed that anti-Semitic acts were consistently under-reported.
The lack of data on the issue made it harder to tackle the problem, said the report.
The report based its findings on a review of official data compiled by EU member states, and what it called unofficial data collected by civil society organizations.
There was no official data available from two member states, Hungary and Portugal.
Rights groups in Germany noted the link between the surge in anti-Semitism and the COVID-19 pandemic.
In the first months of the pandemic, the Department for Research and Information on Antisemitism Berlin (RIAS), said 44 percent of the incidents it had recorded were linked to the coronavirus.
A federation of Jewish communities in the Czech Republic recorded 874 incidents in 2020, up from 694 the previous year.
Almost all of them were published in the media or online and many concerned anti-Semitic conspiracy theories specifically related to the pandemic, said the report.
"Anti-Semitism is a serious problem," FRA director Michael O'Flaherty said in a statement introducing the report.
"But without the data, we do not know how serious it is."
EU countries needed to encourage reporting of such incidents and improve the recording and collection of the data collection, he added.
"With that we will be better able to tackle hatred and prejudice against Jews."