Several videos of police brutality have emerged during protests over the death of African American George Floyd.
In Buffalo, New York State, two officers were suspended after they were seen shoving an elderly white man to the ground.
And in New York City, police were captured on video roughly handling demonstrators as they ran away.
The reports come hours after a memorial for Floyd in Minneapolis, the city where he died at the hands of police.
His killing, also captured on video, has caused outrage and sparked a wave of protests against racial discrimination and police treatment of African Americans in cities across the US and the world.
The vast majority of demonstrations over the past eight days have been peaceful but some have descended into violence and rioting, with curfews imposed in a number of cities.
In a separate development, police in Arizona released details of the killing of another African American, Dion Johnson, in Phoenix on 25 May, the same day as Floyd.
Johnson was shot dead by state troopers after being found "passed out in the driver's seat" of a car which was partially blocking traffic, a police statement said.
"During the trooper's contact with the suspect, there was a struggle and the trooper fired his service weapon striking the suspect," police said.
The statement was only released after Johnson's family was offered audio of the police dispatch and transportation department video of the incident.
More on George Floyd's death
What do the videos show?
The Buffalo video shows a 75-year-old man approach police officers enforcing a curfew. They then move forward, pushing him back and causing him to fall over and hit his head.
As he lies on the ground, blood is seen pouring from his ear.
The man was taken away in an ambulance and was later found to have suffered a severe head injury.
An initial statement from Buffalo Police Department said the man had "tripped" and fallen during a "skirmish involving protesters", compounding outrage at the incident on social media.
Police spokesman Jeff Rinaldo later attributed the statement to officers not directly involved in the incident, adding that when the video had emerged the two policemen who pushed the demonstrator had been suspended without pay.
On the same evening, a delivery driver in New York City was arrested 27 minutes after the city's curfew had started, despite being a key worker exempt from the curfew.
And in the Williamsburg area of the city, police were filmed charging demonstrators, throwing at least one person to the ground.
Other videos showed a man lying on the ground bleeding from the head, and being arrested.
How have the authorities responded?
On Thursday New York State Governor Andrew Cuomo defended police, saying they were not beating citizens "for no reason", and if they did "it's wrong".
City Mayor Bill de Blasio said the authorities were "doing everything from a perspective of restraint".
But both men have since condemned the incidents which emerged overnight.
"Police officers must enforce – NOT ABUSE – the law," he said.
Meanwhile Mayor de Blasio said he had complained to the city police department after seeing the video of the arrest of the delivery worker.
What is the background?
The incidents happened as police enforced curfews in dozens of cities across the US after a wave of protests sparked by George Floyd's death.
Floyd, 46, was stopped by police investigating the purchase of cigarettes with counterfeit money on 25 May in Minneapolis.
A video showed him being arrested and a white police officer continuing to kneel on his neck for several minutes even after he pleaded that he could not breathe.
Protests erupted and have continued since, across many US cities and also internationally, with rallies on Wednesday in Australia, France, the Netherlands and in the UK, where thousands gathered in central London.
A rally in the Australian city of Sydney has been refused permission by a court, amid fears of coronavirus health risks. Thousands had been expected to attend.
Floyd's death follows the high-profile cases of Michael Brown in Ferguson, Missouri; Eric Garner in New York; and others that have driven the Black Lives Matter movement in recent years.
For many, the outrage over Floyd's death also reflects years of frustration over socio-economic inequality and discrimination.
Protests over the death continued in dozens of cities on Thursday despite widespread curfews.
They followed a memorial service attended by hundreds, who stood in silence for eight minutes and 46 seconds, the amount of time Floyd was alleged to have been on the ground under the control of police in Minneapolis.
A lawyer for George Floyd told the service a "pandemic of racism" had led to his death.
Giving the eulogy, civil rights activist the Reverend Al Sharpton said it was time to stand up and say "get your knee off our necks".
US protests timeline
George Floyd dies after being arrested by police outside a shop in Minneapolis, Minnesota. Footage shows a white officer, Derek Chauvin, kneeling on Mr Floyds neck for several minutes while he is pinned to the floor. Mr Floyd is heard repeatedly saying "I cant breathe". He is pronounced dead later in hospital.
Four officers involved in the arrest of George Floyd are fired. Protests begin as the video of the arrest is shared widely on social media. Hundreds of demonstrators take to the streets of Minneapolis and vandalise police cars and the police station with graffiti.
Protests spread to other cities including Memphis and Los Angeles. In some places, like Portland, Oregon, protesters lie in the road, chanting "I cant breathe". Demonstrators again gather around the police station in Minneapolis where the officers involved in George Floyds arrest were based and set fire to it. The building is evacuated and police retreat.
President Trump blames the violence on a lack of leadership in Minneapolis and threatens to send in the National Guard in a tweet. He follows it up in a second tweet with a warning "when the looting starts, the shooting starts". The second tweet is hidden by Twitter for "glorifying violence".
A CNN reporter, Omar Jimenez, is arrested while covering the Minneapolis protest. Mr Jimenez was reporting live when police officers handcuffed him. A few minutes later several of his colleagues are also arrested. They are all later released once they are confirmed to be members of the media.
Derek Chauvin charged with murder