A national coalition of activists on Tuesday rejected calls to suspend anti-police protests in New York after two officers were murdered and called for a mass demonstration on New Year's Eve.
America's largest city has been left in shock by the killings of Wenjian Liu, 32, and Rafael Ramos, 40, shot in the head as they sat in their patrol car in broad daylight in Brooklyn on Saturday.
Police said shooter Ismaaiyl Brinsley had a clear anti-police bias and posted Instagram comments that were anti-government and referenced two unarmed black men killed recently by police.
Cities across the United States have seen weeks of protests over the killings and decisions not to prosecute white officers responsible for recent deaths in New York and Ferguson, Missouri.
But on Monday embattled mayor Bill De Blasio urged New Yorkers to suspend protests until after Ramos and Liu are buried as he sought to defuse tensions that police have likened to the crime-ridden 1970s.
While Ramos's funeral will take place on Saturday, no date has yet been announced for Liu's with relatives due to arrive from China.
The Stop Mass Incarceration Network on Tuesday braved rain outside City Hall, where the U.S. and New York flags stood at half mast to mourn the slain officers, to defy calls for a moratorium.
"They have no right to tell us that we should back off our protests and we should silence our voices. Our voices must be heard," network co-founder Carl Dix told reporters.
"Our stance should be as long as these murders by police happen, as long as the criminal justice system refuses to indict and convict any of these killer cops, then our resistance must go on."
The group called for a protest march on New York's iconic Times Square, where thousands traditionally celebrate New Year's Eve on a live televised program watched by millions around the world.
"We're here today to call on people to rock in the New Year with resistance to police murder. No New Year under this old system," said activist Travis Morales, urging protesters to take to the streets on Dec. 31.
The protesters condemned a prosecutor's decision in Milwaukee on Monday not to charge a white officer who shot dead a black man he was trying to search in April. The officer has already been fired.
Recent protests have focused on decisions by grand juries not to prosecute the white officers who shot dead 18-year-old Michael Brown in Ferguson, Missouri, in August and used a fatal chokehold on father-of-six Eric Garner in New York in July.
Sumumba Sobukwe said his group, Occupy Wall Street, were supporting a planned shutdown of 5th Avenue, one of New York's busiest shopping districts, at 5p.m. on Tuesday.
"It's not as a disrespect to any life but it's also to say we've had countless people killed by the police and there's been no calls for a suspension on that," Sobukwe said.
He said the shutdown had been called months earlier and said his group does not condone violence.
"These actions are being used as a pretext to attack our movement and constitutional right to free speech and assembly," he said.
De Blasio, who has biracial children, came under a stream of criticism after telling reporters that he had counseled his teenage son Dante to take extra care when dealing with officers.