NEW YORK (REUTERS) - New York City police are expected to turn out in force this weekend at a wake and funeral for the second of two officers slain in an ambush last month that has further strained relations between the rank and file and Mayor Bill de Blasio.

Wenjian Liu is believed to be the first Chinese-American police officer killed in the line of duty in New York City

Services in his memory will take place in Brooklyn, not far from where he lived with his wife of two months and his parents.

Two weeks ago, the funeral for his partner, Rafael Ramos, was among the largest in the history of the New York Police Department, with more than 20,000 officers from around the country filling the streets surrounding the church.

When Mr de Blasio began to address the congregation inside, many uniformed officers turned their backs to television monitors set up outside, in a gesture of disdain for the liberal mayor for his criticisms of police policies.

Liu, 32, and Rafael Ramos, 40, were shot to death on Dec 20 as they sat in their squad car in Brooklyn. Their killer, Ismaaiyl Brinsley, who killed himself soon after, had said he was seeking to avenge the deaths this summer of two unarmed black men at the hands of white police officers.

The ambush of Liu and Ramos further frayed relations between the rank and file and Mr de Blasio, who vowed to end the New York Police Department's stop-and-frisk policy when he ran for office in 2013.

The mayor, who has a biracial son, also offered qualified support for the wave of protests triggered late last year by the black men's deaths in New York and Missouri.

SHOW RESPECT

New York Police Commissioner Bill Bratton and others have criticised those officers who turned their backs on Mr de Blasio, saying the gesture was inappropriate. He urged officers to show respect for the mayor this weekend at services for Liu.

In a sign of the police force's broadening ethnic diversity, observances are expected to meld Chinese and Buddhist customs with the usual traditions of an NYPD funeral, which date to a time when Roman Catholic men of Irish or Italian descent dominated the force.

Mr Ed Mullins, president of the Sergeants Benevolent Association, one of several city police unions, was among those who turned their backs on Mr de Blasio as the mayor arrived at the hospital where Liu and Ramos were declared dead.

Mr Mullins said he did not know whether officers intended to repeat the gesture at Liu's funeral, as thousands of police did last weekend as the mayor began his eulogy for Ramos.

"I don't think I have the right to interfere in their First Amendment rights," Mr Mullins said in a telephone interview on Friday.

Since the ambush of Liu and Ramos, the number of arrests and court summonses in the city has plummeted.

Although they have denied a formal slowdown, union leaders have encouraged members to not skirt department rules that may seem time-consuming, including waiting for backup to arrive, in the interest of safety.

Mr Mullins said he believed police were still responding to emergencies as before, even if they were issuing fewer tickets for minor violations.

"Car stops are a very dangerous aspect of police work," he said. "The public should be happy."