https://www.bbc.com/news/world-us-canada-52478414
In response to reports of the mass gathering of mourners, Mr de
Blasio warned "the Jewish community" that police would make arrests.
The city leader was accused of anti-Semitism for his comments.
The Hasidic Jews were mourning a late rabbi at the service in the Williamsburg, Brooklyn, neighbourhood.
"If in my passion and in my emotion I said something that was hurtful, I'm sorry about that," Mr de Blasio said.
"I have no regrets about calling out this danger and saying we're going to deal with it very, very aggressively."
Images shared online by journalists show a large gathering of people attending the funeral on Tuesday night.