JTA — Leaders of a Polish nationalist movement said a historian’s claims that Jews helped perpetrate the Holocaust were “factual” and “necessary.”

The historian who made the claims, Krzysztof Jasiewicz, was “far from politically correct but his statements are supported by historical facts,” Robert Winnicki, president of the All-Polish Youth, said in a statement published Tuesday on the website of the ultra-nationalist organization, which has a few thousand registered members.

Artur Zawisza, a former lawmaker in the Polish parliament, is quoted as telling the news site NaTemat.pl that Jasiewicz “said too much common sense that has long been present in the literature.” He said the historian’s claims were a “necessary part of open debate.”...