More than 150 protesters were arrested in California overnight after shutting down a major freeway and stopping an Amtrak train as nationwide demonstrations against police use of deadly force on minorities continued for a third night.
Hundreds of people marched through the college town of Berkeley for a third night a row on Monday, local media reported.
California Highway Patrol spokesman Daniell Hill said several hundred people stormed onto Interstate 80 in the town near San Francisco late Monday, snarling traffic in both directions.
Protesters threw rocks and other objects at officers, Hill said. More than 150 people were arrested, mostly for resisting or obstructing an officer, he added.
Earlier, dozens of protesters stopped an Amtrak train in Berkeley by lying on the tracks or sitting on a sofa placed across the line.
No injuries were reported in either incident.
Marches were held in a number of cities across the United States, including Phoenix and Seattle, where demonstrations remained largely peaceful.
In downtown Phoenix, about 200 protesters marched to police headquarters over the killing of another unarmed black man by a white officer in what authorities described as a struggle last week.
About 300 protesters in New York City blocked streets outside the Barclays Center sports arena, where the National Basketball Association's Cleveland Cavaliers were playing against the Brooklyn Nets.
The demonstrators chanted the now-famous phrase "I Can't Breathe," the last words spoken by Eric Garner, a 43-year-old man who died in July after being placed in a chokehold by police officer Daniel Pantaleo and forced to the ground in an incident captured on video.
Inside the arena, Cavaliers' superstar LeBron James and other players wore T-shirts emblazoned with the phrase during pre-game warm ups.
Angry protests erupted last week over the deaths of Garner and Michael Brown, an unarmed teenager in Ferguson, Missouri who was shot to death in August after a street confrontation with officer Darren Wilson.
Behind the protests
A grand jury's decision Nov. 24 not to indict Wilson sparked angry and violent protests for several nights in Ferguson. A grand jury decision Dec. 3 in the New York case sparked another series of nationwide protests.
On Monday, New York State Attorney General Eric Schneiderman said he was seeking the power to investigate all police killings of unarmed civilians in the state. It remained unclear whether New York Governor Andrew Cuomo would grant Schneiderman such powers.
In an interview with Black Entertainment Television Monday, President Barack Obama said that blacks do not exaggerate when they talk about such situations, and said racism is "deeply rooted" in U.S. society.
The president also said what is happening today cannot be equated to what happened 50 years ago, when police in some parts of the South used fire hoses, vicious dogs and batons to break up civil rights marches.
Obama urged young people to be persistent and not give up in bringing about change in the criminal justice system, because progress comes in steps and increments.
"When you are dealing with something as deeply rooted as racism or bias in any society, you've got to have vigilance, but you have to recognize that it's going to take some time and you just have to be steady," Obama said.
Protesters have also been angered at a handful of other deaths of unarmed African-Americans at the hands of white police officers.
In Cleveland, Ohio, a police officer who reportedly had a poor performance record, gunned down a 12-year-old black boy in a public park as he waved what turned out to be a toy pistol.
Rookie New York City police officer Peter Laing, who is white, shot dead a black man named Akai Gurley in a stairwell of a Brooklyn apartment house last month.
Police officials said Gurley was not a crime suspect and was killed when the officer's gun accidentally went off. But a New York newspaper reported that Laing waited instead of immediately calling an ambulance.
The Brooklyn district attorney said a grand jury will consider charges against Laing.
Some material for this report came from Reuters and AP.