NEW YORK (AFP) - New York's mayor sparked controversy after he broke up crowds gathering for a rabbi's funeral and threatened arrests, with religious leaders accusing him of unfairly targeting the Jewish community.

Thousands of Orthodox Hasidic Jews, according to the mayor's estimate, lined streets in the Williamsburg area of Brooklyn late on Tuesday to pay their respects to 73-year-old Chaim Mertz, who died from Covid-19.

Mayor Bill de Blasio took to Twitter to describe how he had personally forced the mourners to disperse, saying there was "zero tolerance" for large events while the city fights coronavirus.

"My message to the Jewish community, and all communities, is this simple: the time for warnings has passed," he wrote.

"I have instructed the NYPD to proceed immediately to summons or even arrest those who gather in large groups. This is about stopping this disease and saving lives. Period."

De Blasio was slammed for specifically mentioning the Jewish community and for appearing to lump all worshippers of the diverse faith together when it was only some members of one sect in attendance.

"I saw the troubling photos from the funeral, but singling out the entire Jewish community for possible arrest sends a shiver down our collective spine," tweeted Ted Deutch, chairman of the House of Representatives ethics committee.

"Mr Mayor, when you've got a message for 'all communities', we Jews are covered," he added.

Prominent Republican senator Ted Cruz tweeted: "Laws should be enforced neutrally w/o targeting religious faith."

De Blasio on Wednesday said he apologised if his choice of words had offended anyone but doubled down on denouncing the gathering.

"I have no regrets about calling out this danger," he said, adding that he would deal "very, very aggressively" with social distancing violations.

Social media users pointed out that large groups of people had also gathered on Tuesday to watch US military fighter jets fly over New York in tribute to coronavirus health care staff.

The Orthodox Jewish Public Affairs Council (OJPAC) tweeted photos of crowds watching the planes.

"@NYCMayor BDB was wrong to rush to Williamsburg for a thing (lack of social distancing) that has gone on all day across the city, and then he was wrong for his tweet," OJPAC said.

It accused de Blasio of "singling out" all of New York City's 1.1 million Jews, the largest Jewish community outside of Israel, when "a few hundred (mostly teens)" had attended the funeral.

The headquarters for the Satmar Hasidic group wrote on Twitter that the funeral had been held with the approval of New York police, who brought barriers to block off the road.

NYPD Commissioner Dermot Shea said local police officers were in contact with members about the gathering but did not say whether any authorisation had been given.