Jewish groups intensified criticism on Tuesday of Rudy Giuliani, the former New York mayor turned president’s lawyer and freelancing Ukrainian envoy, after he attacked the Jewish financier, philanthropist and Holocaust survivor George Soros for being “hardly a Jew” and failing to attend synagogue.

Giuliani also asserted he was “more of a Jew than Soros” and repeated a claim that the former US ambassador to Ukraine, Marie Yovanovitch, who testified in Donald Trump’s impeachment inquiry, was controlled by the financier.

The Anti-Defamation League CEO, Jonathan Greenblatt, furiously rebuked Giuliani, who is of Italian descent and was raised Roman Catholic, describing his comments as “baffling and offensive” and a “dog whistle to hardcore antisemites and white supremacists who believe this garbage”.

Greenblatt called on Giuliani to “apologize and retract his comments immediately”.

The central thrust and larger offense caused by Giuliani’s comments, which were made during an interview with New York magazine, the group argued, was to repeat a trope about the financier controlling political appointments and events.

Soros is widely recognized for funding progressive political and social causes.

To those accusations Greenblatt tweeted: “Opposing Soros isn’t what’s #antiSemitic. Saying that he controls ambassadors, employs FBI agents and isn’t ‘Jewish enough’ to be demonized is.”

In an article published on its website in October, the ADL said: “In far-right circles worldwide, Soros’ philanthropy often is recast as fodder for outsized conspiracy theories, including claims that he masterminds specific global plots or manipulates particular events to further his goals.”

The American Jewish Committee, an advocacy group, tweeted a stinging riposte to Giuliani, saying: “You’re entitled to your views, and to denouncing his [Soros’s]. But it’s offensive to deny anyone’s faith, and worse to endorse classically antisemitic conspiracy theories.”

No, Mayor, you’re not “more of a Jew than Soros.” You’re entitled to your views, and to denouncing his. But it’s offensive to deny anyone’s faith, and worse to endorse classically antisemitic conspiracy theories.https://t.co/NnXrK2MRDt — American Jewish Committee (@AJCGlobal) December 23, 2019

In an interview with the Guardian last month, Soros said repeated attacks against him from the right, both in their intensity and number, served to sustain him.

“It challenges me and therefore it energises me,” he said. “When I look at the list of people, or movements, or countries who are attacking me, it makes me feel I must be doing something right. I’m proud of the enemies I have.”

The 86-year-old Soros, who survived the Nazi occupation of his native Hungary, was said by Giuliani to be behind ambassadorial appointments and “employing the FBI agents”, in an unexplained claim that the magazine described as him “weaving one made-up talking point into another and another”.

George Soros: ‘I’m proud of the enemies I have.’ Photograph: Ronald Zak/AP

Challenged on his views, Giuliani retorted: “Don’t tell me I’m antisemitic if I oppose him.”

“Soros is hardly a Jew,” he continued. “I’m more of a Jew than Soros is. I probably know more about – he doesn’t go to church, he doesn’t go to religion – synagogue. He doesn’t belong to a synagogue, he doesn’t support Israel, he’s an enemy of Israel.”

But Giuliani shows no sign of retracting or moderating his comments. Asked by NBC News if his remarks were seriously intended, the former mayor texted: “I’m more Jewish than half my friends.”

Soros, who emigrated to the UK in 1947 where he attended the London School of Economics is believed to have a net worth of around $8bn, having given around $32bn to his philanthropic agency, the Open Society Foundations, known for supporting global democratic causes.

In the US alone, the group is reported to have given $33m in financial support to civil rights and social justice organizations, among them efforts to bring justice to bear in several high-profile killings of African American men by law enforcement.

A spokeswoman for Soros’s foundations, Laura Silber, on Tuesday called Giuliani’s remarks “contemptible,” tweeting that they “reflect his toxic campaign of misinformation and falsehoods aimed at distracting from the gravity of the charges facing the president”.