New York state's top prosecutor is seeking the power to investigate all police killings of unarmed civilians in his state.
Attorney General Eric Schneiderman said action was need to address a "crisis of confidence" in the US criminal justice system.
His statement comes after sometimes violent US protests over two grand juries' moves to clear officers in the deaths of unarmed black men.
Cities across the United States have seen large protests in recent nights following a grand jury's decision not to charge a New York police officer in the July killing of 43-year-old Eric Garner.
An unarmed black father of six, Mr Garner died after police put him in a banned chokehold.
The decision in the Garner case came a little more than a week after a Missouri grand jury cleared a white officer in the August fatal shooting of an unarmed black teenager, Michael Brown.
"The horrible events surrounding the death of Eric Garner have revealed a deep crisis of confidence in some of the fundamental elements of our criminal justice system," Mr Schneiderman said in a statement.
"Nothing could be more critical for both the public and the police officers who work tirelessly to keep our communities safe than acting immediately to restore trust."
Mr Schneiderman said he was seeking a temporary executive order from state Governor Andrew Cuomo shifting authority to investigate police killings of unarmed civilians to the state from local prosecutors, who work closely with local police, until lawmakers could pass a more permanent measure.
US Attorney General Eric Holder, whose office is investigating the Garner case, plans to announce a set of changes to federal law enforcement guidelines intended to set an example for local police, according to a Justice Department official.
Cold, wet weather in New York brought smaller crowds of protesters over the weekend, though organisers have vowed fresh actions today as Britain's Prince William and his wife visit the city.
In Cleveland, where the US Justice Department last week said police routinely use excessive force, Samantha Rice, the mother of a 12-year-old African American boy shot dead by police last month, spoke to media for the first time since her son's death.
Tamir Rice was shot while carrying a pellet gun that was a replica of a real gun.
The boy's family has filed a federal civil rights lawsuit against the city and the two officers involved, one who shot Tamir on 22 November and one who was driving the police car.
"I'm actually looking for conviction," Ms Rice told reporters.
"Tamir was a bright child, he had a promising future and he was very talented in all sports, soccer, basketball, football. He was my baby."
Police in Berkeley, California, today said they made five arrests during last night’s protests, when a crowd of more than 500 people hurled objects at police and a number of shops were looted.
One protester who tried to prevent the looting was assaulted, police said.
The two nights of looting and rock-throwing on the West Coast contrasted with mostly peaceful demonstrations elsewhere around the United States following the decision not to indict New York Police Department officer Daniel Pantaleo for the July death of Mr Garner.
Five #CHP patrol vehicles sustained damage when individuals from the protest turned violent. pic.twitter.com/6l7Doi5IEz
— CHP Golden Gate (@CHP_GoldenGate) December 8, 2014While no criminal charges have been brought, and Mr Schneiderman's request would not apply to the Garner case or any other case preceding the executive order he has sought, the NYPD is conducting an internal investigation into the case.
The inquiry into whether Mr Pantaleo broke any department rules could take four months, officials have said.
The Justice Department is also investigating the case.
Smaller protests were held in Seattle, Chicago and Miami yesterday.
The outcry over the recent killings spread to NFL stadiums as well.
Detroit Lions running back Reggie Bush was among several players donning pre-game practice jerseys reading "I can't breathe," Mr Garner's dying words.
