NEW YORK (AP) -- New York's mayor on Monday called for protests and political debate to pause until after funerals are held for two officers shot and killed inside their patrol car this weekend by a man vowing retaliation for the deaths of black men at the hands of white police.

"I think it's important that regardless of people's viewpoints that everyone step back," Mayor Bill de Blasio said in a speech at the Police Athletic League. "I think it's a time for everyone to put aside political debates, put aside protests, put aside all of the things that we will talk about in all due time."

A NYPD officer looks over a makeshift memorial near the site where fellow officers Rafael Ramos and Wenjian Liu were murdered in the Brooklyn. (AP Photo/Seth Wenig)
A NYPD officer looks over a makeshift memorial near the site where fellow officers Rafael Ramos and Wenjian Liu were murdered in the Brooklyn. (AP Photo/Seth Wenig)
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Officers Wenjian Liu and Rafael Ramos were ambushed Saturday afternoon by a 28-year-old who wrote in an Instagram post that he would put "wings on pigs." The suspect, Ishmaaiyl Brinsley was black; the slain New York Police Department officers were Hispanic and Asian.

The killings came at a tense time as police nationwide are being criticized following Eric Garner's death in a New York officer's chokehold and 18-year-old Michael Brown's fatal shooting in Ferguson, Missouri. Protests erupted in recent weeks after grand juries declined to charge the officers involved. On Monday, a prosecutor said a white Milwaukee police officer who was fired after he fatally shot a mentally ill black man in April won't face criminal charges.

De Blasio said it was time to focus on the grieving families of the officers. He and Police Commissioner William Bratton met with the families on Monday.

"There's a lot of pain. It's so hard to make sense of it - how one deeply troubled, violent individual could do this to these good families," de Blasio said. "And I think it's a time for everyone to take stock that there are things that unite us, there are things that we hold dear as new Yorkers, as Americans."

New York Gov. Andrew Cuomo also urged people on both sides to tone down their rhetoric, calling in a WNYC-AM radio interview for "rational, sober conversation" later to consider reforms.

Meanwhile, big-city police departments and union leaders around the country were warning the rank and file to wear bulletproof vests and avoid making inflammatory posts on social media.

A union-generated message at the 35,000-officer NYPD warned officers that they should respond to every radio call with two cars - "no matter what the opinion of the patrol supervisor" - and not make arrests "unless absolutely necessary." The president of the detectives' union told members in a letter to work in threes when out on the street, wear bulletproof vests and keep aware of their surroundings.

Another directive warned officers in Newark, New Jersey, not to patrol alone and to avoid people looking for confrontations. At the same time, a memo from an NYPD chief asked officers to limit their comments "via all venues, including social media, to expressions of sorrow and condolence."

In Philadelphia, Police Commissioner Charles Ramsey urged the leaders of protests over the deaths of Garner and Brown to "call for calm and not let this escalate any further." In Boston, Police Commissioner William Evans said police issued an alert warning officers about the New York City killings and added that the department had issued several alerts following the Ferguson grand jury's decision.

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