Some police officers turn their backs as Mayor Bill de Blasio speaks during the funeral of New York Police Department Officer Wenjian Liu on Sunday in Brooklyn. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street.

NEW YORK — Police officers from around the U.S. joined grieving family members as they mourned a 32-year-old immigrant who realized his dream of being an NYPD officer but was gunned down in his squad car.

New York City Mayor Bill de Blasio and Police Commissioner William Bratton eulogized Officer Wenjian Liu on Sunday as an incarnation of the American dream: a man who had emigrated from China at age 12 and devoted himself to helping others in his adopted country.

But thousands of officers turned their backs as de Blasio spoke, repeating a stinging display of scorn for a mayor who many officers say is anti-police.

The gesture among officers watching the mayor’s speech on a screen outside a Brooklyn funeral home added to tensions between de Blasio and rank-and-file police even as he sought to mollify them.

Liu had served as a policeman for seven years and was married just two months when he was killed with his partner, Officer Rafael Ramos, on Dec. 20.

Liu’s weeping father, Wei Tang Liu, said that his only child used to call after every shift to say: “I’m coming home today. You can stop worrying now.”

Dignitaries including FBI Director James Comey and members of Congress joined police officers and other mourners at a service that blended police tradition with references to Buddha’s teachings.

“When one of us loses our lives, we have to come together,” said Officer Lucas Grant of the Richmond County Sheriff’s Office in Augusta, Ga.

After hundreds of officers turned their backs to a screen where de Blasio’s remarks played during Ramos’ funeral last week, Bratton sent a memo urging respect, declaring “a hero’s funeral is about grieving, not grievance.”

But some officers and police retirees said they still felt compelled to spurn the mayor. Police union leaders have said he contributed to an environment that allowed the officers’ slayings by supporting protests following the police killings of Eric Garner on Staten Island and Michael Brown in Ferguson, Mo.

“The mayor has no respect for us. Why should we have respect for him?” said retired New York Police Department Detective Camille Sanfilippo, who was among those who turned their backs Sunday.

The officers’ killer, Ismaaiyl Brinsley, committed suicide after the daytime ambush in Brooklyn.

The mayor got a respectful reception among police officials inside the funeral home.