Law enforcement officers turn their backs on a live video monitor showing New York City Mayor Bill de Blasio as he speaks at the funeral of slain New York Police Department (NYPD) officer Rafael Ramos near Christ Tabernacle Church in the Queens borough of New York Dec 27, 2014. [Photo/Agencies]

NEW YORK - Tens of thousands of police from cities across the United States filled a New York City church and nearby streets on Saturday for the funeral of one of two policemen shot by a man who said he was avenging the killing of unarmed black men by police.

The service for Rafael Ramos was one of the largest police funerals in the city's history, with US Vice President Joe Biden among the dignitaries. But the tradition-bound ceremony was marked by an unusual protest against Mayor Bill de Blasio.

As he rose to deliver the customary mayoral eulogy, thousands of uniformed officers outside silently turned their backs on him in a pointed display of disrespect as his image filled the large screens broadcasting the service.

Angered by the mayor's qualified sympathy for nationwide demonstrations calling for police reform, some New York police officers had similarly shunned de Blasio as he arrived a week ago at the hospital where Ramos and his police partner, Wenjian Liu, were declared dead.

"He believed in protecting others," de Blasio said as he stood behind Ramos' coffin, which was draped in the police department's flag and bathed in blue light, "and those who are called to protect others are a special breed."

Singled out for their uniforms, the slaying of Ramos, 40, and Liu, 32, as they sat in their patrol car has become a rallying point for police and their supporters around the country, beleaguered by months of street protests accusing police of racist practices.

Offering a counter-narrative to the anti-police chants at many protests, Vice President Biden made the first of several speeches that touched on the marked increase in the racial diversity of the city's police force, which only a few decades ago was almost entirely white.

"I believe that this great police force of this incredibly diverse city can and will show the nation how to bridge any divide," Biden said during the service at Christ Tabernacle Church in the suburban Queens neighborhood in which Ramos lived with his wife, Maritza, and their two teenage sons.

New York Governor Andrew Cuomo said the department had officers hailing from more than 50 different nations and included speakers of 64 languages. He went on to criticize some of the protesters who have held rallies in the city on a nearly daily basis.

"The NYPD protected the right of free speech even though they themselves were the targets of false and abusive tirades by some," he said.