Thousands of protesters have taken to the streets in US cities for a second night to protest against a grand jury's decision not to charge a white New York City police officer accused of killing an unarmed black man in a chokehold.

The case of Eric Garner - combined with the decision by a grand jury last week not to charge the white officer who shot and killed an unarmed black teenager in Ferguson, Missouri - have re-ignited debate over a US law enforcement system widely perceived to unfairly target African Americans and other minorities.

Al Jazeera's Kristen Saloomey, reporting from New York on Thursday, said thousands had gathered in lower Manhattan for a rally amid a massive police presence, with helicopters monitoring the crowds from the air.

"Emotions have been running high at the protests and there is concern that things could run out of control," she said. "What was initially a minority issue has become a national movement."

Police said 83 people were arrested a day earlier, mostly on disorderly conduct charges, in protests held after the grand jury's decision was announced.

In Washington, DC, protesters blocked a major highway, and at a university campus in Austin, about 200 protesters held a so-called "die-in" demonstration, simulating being dead.

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Garner, 43, was killed in July in an apparent chokehold by police officer Daniel Pantaleo after he stopped him on suspicion of selling loose, untaxed cigarettes, which is illegal.

The incident was captured in a video that showed Garner pressed on the ground by police officers while Pantaleo wrapped his arm around Garner's neck.

Garner kept groaning "I can't breathe" as police officers firmly held him to the ground.

Rights leaders critical

About 20 civil rights leaders met behind closed doors on Thursday at the New York City headquarters of Reverend Al Sharpton's National Action Network to plan a response to the jury's decision.

Sharpton, one of the country's most outspoken civil rights activists, said a civil rights summit would be held following a December 13 march in Washington on racial justice.

National Urban League President Marc Morial said the lack of an indictment in Garner's death was "a travesty of justice".

US Attorney General Eric Holder has pledged a Justice of Department investigation into the case that he said would be "independent, thorough, fair and expeditious".

The investigation is likely to focus on whether Pantaleo employed a chokehold, banned by New York Police Department regulations, in restraining Garner

Stuart London, the police officer's lawyer, said in an interview that Pantaleo testified to the grand jury that he never put pressure on Garner's neck. Instead, Pantaleo said he used a proper takedown technique, London said.

That account was echoed by Patrick Lynch, the president of the patrolmen's union, who called Pantaleo a "model" officer at a press conference.

The city's medical examiner has said police officers killed Garner by compressing his neck and chest, adding that Garner's asthma and obesity had contributed to his death.

New York City Mayor Bill de Blasio, who took office in January promising to improve relations between minority New Yorkers and police, told reporters on Thursday the city's thousands of patrol officers would undergo extensive retraining.

"The relationship between police and community has to change," he told a news conference. "People need to know that black lives and brown lives matter as much as white lives."

Source: Al Jazeera and agencies