New York City Mayor Bill de Blasio (C) speaks while New York Police Commissioner Bill Bratton listens with other officers during a news conference in New York January 5, 2015. [Photo/Agencies]

De Blasio called the many hundreds of police officers who have since turned their backs to him at the policemen's funerals and other events "disrespectful" to the city.

The drop in police activity since the ambush has continued into a second week. The number of arrests across the city was down more than half in the week ending Sunday compared with the same week the previous year, to 2,401 from 5,448, police said, confirming data first reported in the New York Times on Monday.

The number of criminal court summonses dropped more than 90 percent to 347 from 4,077.

"Am I overly concerned at this particular point?" Bratton replied when asked if police were turning a blind eye to some crimes. "Talk to me a little later in the week once I have a clearer idea of the impacts of the demonstrations, the funerals."

De Blasio, who has expressed impatience with what he calls "divisive" news coverage of his problems with his police department, was keen not to dwell on the topic.

"I want to get us back to questions on this presentation," he said, pointing to charts showing the steep fall in crime since 1993. "This is breathtaking, the information we have here."