George Arzt, a political consultant and former press secretary for Mayor Edward I. Koch who was a reporter and City Hall bureau chief for The Post from 1968 to 1986, noted that Mr. Koch’s chief antagonists were investigative reporters from The Village Voice, namely Wayne Barrett and Jack Newfield. The two would never get interviews, Mr. Arzt said, “but they were allowed to ask questions” during news conferences.

“No one that I’ve seen before this has gone after a paper as an institution,” he said. “You can’t say everyone on the paper is against me without making them against you. He’s creating his own problem.”

Last month, Mr. de Blasio characterized as “fabricated stuff” a front-page Post article suggesting he had made a high-level appointment at the behest of a donor who has since pleaded guilty to bribery charges. This month, he refused to answer a question from Mr. Gonen about the background of a contractor hired by the city to train correction officers, adding sarcastically that he did not “appreciate your propagandistic newspaper.”

In a telephone interview late Thursday, Mr. de Blasio said it was time to “have this conversation” about The Post, which he described as “a very negative presence in our city” and an “ideological apparatus” with little resemblance to a truth-seeking news operation.

“I think it’s important, as the leader of this city, to say out loud what so many people already know,” he said. “The Post’s approach has gotten worse and worse.”

He said he had not planned the comments he made at the news conference, adding that he would answer questions from Post reporters in the future, provided they were not “in the middle of playing out one of their propaganda strategies.”

The news conference on Thursday included several exchanges in which the mayor appeared exasperated with questions from various reporters about transparency and overlapping investigations into his administration. All the while, he ignored the raised hand of Mr. Gonen.